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| -rw-r--r-- | doc/driver-model/spi-howto.txt | 594 |
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diff --git a/doc/driver-model/spi-howto.txt b/doc/driver-model/spi-howto.txt new file mode 100644 index 0000000..719dbd5 --- /dev/null +++ b/doc/driver-model/spi-howto.txt @@ -0,0 +1,594 @@ +How to port a SPI driver to driver model +======================================== + +Here is a rough step-by-step guide. It is based around converting the +exynos SPI driver to driver model (DM) and the example code is based +around U-Boot v2014.10-rc2 (commit be9f643). + +It is quite long since it includes actual code examples. + +Before driver model, SPI drivers have their own private structure which +contains 'struct spi_slave'. With driver model, 'struct spi_slave' still +exists, but now it is 'per-child data' for the SPI bus. Each child of the +SPI bus is a SPI slave. The information that was stored in the +driver-specific slave structure can now be port in private data for the +SPI bus. + +For example, struct tegra_spi_slave looks like this: + +struct tegra_spi_slave { + struct spi_slave slave; + struct tegra_spi_ctrl *ctrl; +}; + +In this case 'slave' will be in per-child data, and 'ctrl' will be in the +SPI's buses private data. + + +0. How long does this take? + +You should be able to complete this within 2 hours, including testing but +excluding preparing the patches. The API is basically the same as before +with only minor changes: + +- methods to set speed and mode are separated out +- cs_info is used to get information on a chip select + + +1. Enable driver mode for SPI and SPI flash + +Add these to your board config: + +#define CONFIG_DM_SPI +#define CONFIG_DM_SPI_FLASH + + +2. Add the skeleton + +Put this code at the bottom of your existing driver file: + +struct spi_slave *spi_setup_slave(unsigned int busnum, unsigned int cs, + unsigned int max_hz, unsigned int mode) +{ + return NULL; +} + +struct spi_slave *spi_setup_slave_fdt(const void *blob, int slave_node, + int spi_node) +{ + return NULL; +} + +static int exynos_spi_ofdata_to_platdata(struct udevice *dev) +{ + return -ENODEV; +} + +static int exynos_spi_probe(struct udevice *dev) +{ + return -ENODEV; +} + +static int exynos_spi_remove(struct udevice *dev) +{ + return -ENODEV; +} + +static int exynos_spi_claim_bus(struct udevice *dev) +{ + + return -ENODEV; +} + +static int exynos_spi_release_bus(struct udevice *dev) +{ + + return -ENODEV; +} + +static int exynos_spi_xfer(struct udevice *dev, unsigned int bitlen, + const void *dout, void *din, unsigned long flags) +{ + + return -ENODEV; +} + +static int exynos_spi_set_speed(struct udevice *dev, uint speed) +{ + return -ENODEV; +} + +static int exynos_spi_set_mode(struct udevice *dev, uint mode) +{ + return -ENODEV; +} + +static int exynos_cs_info(struct udevice *bus, uint cs, + struct spi_cs_info *info) +{ + return -ENODEV; +} + +static const struct dm_spi_ops exynos_spi_ops = { + .claim_bus = exynos_spi_claim_bus, + .release_bus = exynos_spi_release_bus, + .xfer = exynos_spi_xfer, + .set_speed = exynos_spi_set_speed, + .set_mode = exynos_spi_set_mode, + .cs_info = exynos_cs_info, +}; + +static const struct udevice_id exynos_spi_ids[] = { + { .compatible = "samsung,exynos-spi" }, + { } +}; + +U_BOOT_DRIVER(exynos_spi) = { + .name = "exynos_spi", + .id = UCLASS_SPI, + .of_match = exynos_spi_ids, + .ops = &exynos_spi_ops, + .ofdata_to_platdata = exynos_spi_ofdata_to_platdata, + .probe = exynos_spi_probe, + .remove = exynos_spi_remove, +}; + + +3. Replace 'exynos' in the above code with your driver name + + +4. #ifdef out all of the code in your driver except for the above + +This will allow you to get it building, which means you can work +incrementally. Since all the methods return an error initially, there is +less chance that you will accidentally leave something in. + +Also, even though your conversion is basically a rewrite, it might help +reviewers if you leave functions in the same place in the file, +particularly for large drivers. + + +5. Add some includes + +Add these includes to your driver: + +#include <dm.h> +#include <errno.h> + + +6. Build + +At this point you should be able to build U-Boot for your board with the +empty SPI driver. You still have empty methods in your driver, but we will +write these one by one. + +If you have spi_init() functions or the like that are called from your +board then the build will fail. Remove these calls and make a note of the +init that needs to be done. + + +7. Set up your platform data structure + +This will hold the information your driver to operate, like its hardware +address or maximum frequency. + +You may already have a struct like this, or you may need to create one +from some of the #defines or global variables in the driver. + +Note that this information is not the run-time information. It should not +include state that changes. It should be fixed throughout the live of +U-Boot. Run-time information comes later. + +Here is what was in the exynos spi driver: + +struct spi_bus { + enum periph_id periph_id; + s32 frequency; /* Default clock frequency, -1 for none */ + struct exynos_spi *regs; + int inited; /* 1 if this bus is ready for use */ + int node; + uint deactivate_delay_us; /* Delay to wait after deactivate */ +}; + +Of these, inited is handled by DM and node is the device tree node, which +DM tells you. The name is not quite right. So in this case we would use: + +struct exynos_spi_platdata { + enum periph_id periph_id; + s32 frequency; /* Default clock frequency, -1 for none */ + struct exynos_spi *regs; + uint deactivate_delay_us; /* Delay to wait after deactivate */ +}; + + +8a. Write ofdata_to_platdata() [for device tree only] + +This method will convert information in the device tree node into a C +structure in your driver (called platform data). If you are not using +device tree, go to 8b. + +DM will automatically allocate the struct for us when we are using device +tree, but we need to tell it the size: + +U_BOOT_DRIVER(spi_exynos) = { +... + .platdata_auto_alloc_size = sizeof(struct exynos_spi_platdata), + + +Here is a sample function. It gets a pointer to the platform data and +fills in the fields from device tree. + +static int exynos_spi_ofdata_to_platdata(struct udevice *bus) +{ + struct exynos_spi_platdata *plat = bus->platdata; + const void *blob = gd->fdt_blob; + int node = bus->of_offset; + + plat->regs = (struct exynos_spi *)fdtdec_get_addr(blob, node, "reg"); + plat->periph_id = pinmux_decode_periph_id(blob, node); + + if (plat->periph_id == PERIPH_ID_NONE) { + debug("%s: Invalid peripheral ID %d\n", __func__, + plat->periph_id); + return -FDT_ERR_NOTFOUND; + } + + /* Use 500KHz as a suitable default */ + plat->frequency = fdtdec_get_int(blob, node, "spi-max-frequency", + 500000); + plat->deactivate_delay_us = fdtdec_get_int(blob, node, + "spi-deactivate-delay", 0); + debug("%s: regs=%p, periph_id=%d, max-frequency=%d, deactivate_delay=%d\n", + __func__, plat->regs, plat->periph_id, plat->frequency, + plat->deactivate_delay_us); + + return 0; +} + + +8b. Add the platform data [non-device-tree only] + +Specify this data in a U_BOOT_DEVICE() declaration in your board file: + +struct exynos_spi_platdata platdata_spi0 = { + .periph_id = ... + .frequency = ... + .regs = ... + .deactivate_delay_us = ... +}; + +U_BOOT_DEVICE(board_spi0) = { + .name = "exynos_spi", + .platdata = &platdata_spi0, +}; + +You will unfortunately need to put the struct into a header file in this +case so that your board file can use it. + + +9. Add the device private data + +Most devices have some private data which they use to keep track of things +while active. This is the run-time information and needs to be stored in +a structure. There is probably a structure in the driver that includes a +'struct spi_slave', so you can use that. + +struct exynos_spi_slave { + struct spi_slave slave; + struct exynos_spi *regs; + unsigned int freq; /* Default frequency */ + unsigned int mode; + enum periph_id periph_id; /* Peripheral ID for this device */ + unsigned int fifo_size; + int skip_preamble; + struct spi_bus *bus; /* Pointer to our SPI bus info */ + ulong last_transaction_us; /* Time of last transaction end */ +}; + + +We should rename this to make its purpose more obvious, and get rid of +the slave structure, so we have: + +struct exynos_spi_priv { + struct exynos_spi *regs; + unsigned int freq; /* Default frequency */ + unsigned int mode; + enum periph_id periph_id; /* Peripheral ID for this device */ + unsigned int fifo_size; + int skip_preamble; + ulong last_transaction_us; /* Time of last transaction end */ +}; + + +DM can auto-allocate this also: + +U_BOOT_DRIVER(spi_exynos) = { +... + .priv_auto_alloc_size = sizeof(struct exynos_spi_priv), + + +Note that this is created before the probe method is called, and destroyed +after the remove method is called. It will be zeroed when the probe +method is called. + + +10. Add the probe() and remove() methods + +Note: It's a good idea to build repeatedly as you are working, to avoid a +huge amount of work getting things compiling at the end. + +The probe method is supposed to set up the hardware. U-Boot used to use +spi_setup_slave() to do this. So take a look at this function and see +what you can copy out to set things up. + + +static int exynos_spi_probe(struct udevice *bus) +{ + struct exynos_spi_platdata *plat = dev_get_platdata(bus); + struct exynos_spi_priv *priv = dev_get_priv(bus); + + priv->regs = plat->regs; + if (plat->periph_id == PERIPH_ID_SPI1 || + plat->periph_id == PERIPH_ID_SPI2) + priv->fifo_size = 64; + else + priv->fifo_size = 256; + + priv->skip_preamble = 0; + priv->last_transaction_us = timer_get_us(); + priv->freq = plat->frequency; + priv->periph_id = plat->periph_id; + + return 0; +} + +This implementation doesn't actually touch the hardware, which is somewhat +unusual for a driver. In this case we will do that when the device is +claimed by something that wants to use the SPI bus. + +For remove we could shut down the clocks, but in this case there is +nothing to do. DM frees any memory that it allocated, so we can just +remove exynos_spi_remove() and its reference in U_BOOT_DRIVER. + + +11. Implement set_speed() + +This should set up clocks so that the SPI bus is running at the right +speed. With the old API spi_claim_bus() would normally do this and several +of the following functions, so let's look at that function: + +int spi_claim_bus(struct spi_slave *slave) +{ + struct exynos_spi_slave *spi_slave = to_exynos_spi(slave); + struct exynos_spi *regs = spi_slave->regs; + u32 reg = 0; + int ret; + + ret = set_spi_clk(spi_slave->periph_id, + spi_slave->freq); + if (ret < 0) { + debug("%s: Failed to setup spi clock\n", __func__); + return ret; + } + + exynos_pinmux_config(spi_slave->periph_id, PINMUX_FLAG_NONE); + + spi_flush_fifo(slave); + + reg = readl(®s->ch_cfg); + reg &= ~(SPI_CH_CPHA_B | SPI_CH_CPOL_L); + + if (spi_slave->mode & SPI_CPHA) + reg |= SPI_CH_CPHA_B; + + if (spi_slave->mode & SPI_CPOL) + reg |= SPI_CH_CPOL_L; + + writel(reg, ®s->ch_cfg); + writel(SPI_FB_DELAY_180, ®s->fb_clk); + + return 0; +} + + +It sets up the speed, mode, pinmux, feedback delay and clears the FIFOs. +With DM these will happen in separate methods. + + +Here is an example for the speed part: + +static int exynos_spi_set_speed(struct udevice *bus, uint speed) +{ + struct exynos_spi_platdata *plat = bus->platdata; + struct exynos_spi_priv *priv = dev_get_priv(bus); + int ret; + + if (speed > plat->frequency) + speed = plat->frequency; + ret = set_spi_clk(priv->periph_id, speed); + if (ret) + return ret; + priv->freq = speed; + debug("%s: regs=%p, speed=%d\n", __func__, priv->regs, priv->freq); + + return 0; +} + + +12. Implement set_mode() + +This should adjust the SPI mode (polarity, etc.). Again this code probably +comes from the old spi_claim_bus(). Here is an example: + + +static int exynos_spi_set_mode(struct udevice *bus, uint mode) +{ + struct exynos_spi_priv *priv = dev_get_priv(bus); + uint32_t reg; + + reg = readl(&priv->regs->ch_cfg); + reg &= ~(SPI_CH_CPHA_B | SPI_CH_CPOL_L); + + if (mode & SPI_CPHA) + reg |= SPI_CH_CPHA_B; + + if (mode & SPI_CPOL) + reg |= SPI_CH_CPOL_L; + + writel(reg, &priv->regs->ch_cfg); + priv->mode = mode; + debug("%s: regs=%p, mode=%d\n", __func__, priv->regs, priv->mode); + + return 0; +} + + +13. Implement claim_bus() + +This is where a client wants to make use of the bus, so claims it first. +At this point we need to make sure everything is set up ready for data +transfer. Note that this function is wholly internal to the driver - at +present the SPI uclass never calls it. + +Here again we look at the old claim function and see some code that is +needed. It is anything unrelated to speed and mode: + +static int exynos_spi_claim_bus(struct udevice *bus) +{ + struct exynos_spi_priv *priv = dev_get_priv(bus); + + exynos_pinmux_config(priv->periph_id, PINMUX_FLAG_NONE); + spi_flush_fifo(priv->regs); + + writel(SPI_FB_DELAY_180, &priv->regs->fb_clk); + + return 0; +} + +The spi_flush_fifo() function is in the removed part of the code, so we +need to expose it again (perhaps with an #endif before it and '#if 0' +after it). It only needs access to priv->regs which is why we have +passed that in: + +/** + * Flush spi tx, rx fifos and reset the SPI controller + * + * @param regs Pointer to SPI registers + */ +static void spi_flush_fifo(struct exynos_spi *regs) +{ + clrsetbits_le32(®s->ch_cfg, SPI_CH_HS_EN, SPI_CH_RST); + clrbits_le32(®s->ch_cfg, SPI_CH_RST); + setbits_le32(®s->ch_cfg, SPI_TX_CH_ON | SPI_RX_CH_ON); +} + + +14. Implement release_bus() + +This releases the bus - in our example the old code in spi_release_bus() +is a call to spi_flush_fifo, so we add: + +static int exynos_spi_release_bus(struct udevice *bus) +{ + struct exynos_spi_priv *priv = dev_get_priv(bus); + + spi_flush_fifo(priv->regs); + + return 0; +} + + +15. Implement xfer() + +This is the final method that we need to create, and it is where all the +work happens. The method parameters are the same as the old spi_xfer() with +the addition of a 'struct udevice' so conversion is pretty easy. Start +by copying the contents of spi_xfer() to your new xfer() method and proceed +from there. + +If (flags & SPI_XFER_BEGIN) is non-zero then xfer() normally calls an +activate function, something like this: + +void spi_cs_activate(struct spi_slave *slave) +{ + struct exynos_spi_slave *spi_slave = to_exynos_spi(slave); + + /* If it's too soon to do another transaction, wait */ + if (spi_slave->bus->deactivate_delay_us && + spi_slave->last_transaction_us) { + ulong delay_us; /* The delay completed so far */ + delay_us = timer_get_us() - spi_slave->last_transaction_us; + if (delay_us < spi_slave->bus->deactivate_delay_us) + udelay(spi_slave->bus->deactivate_delay_us - delay_us); + } + + clrbits_le32(&spi_slave->regs->cs_reg, SPI_SLAVE_SIG_INACT); + debug("Activate CS, bus %d\n", spi_slave->slave.bus); + spi_slave->skip_preamble = spi_slave->mode & SPI_PREAMBLE; +} + +The new version looks like this: + +static void spi_cs_activate(struct udevice *dev) +{ + struct udevice *bus = dev->parent; + struct exynos_spi_platdata *pdata = dev_get_platdata(bus); + struct exynos_spi_priv *priv = dev_get_priv(bus); + + /* If it's too soon to do another transaction, wait */ + if (pdata->deactivate_delay_us && + priv->last_transaction_us) { + ulong delay_us; /* The delay completed so far */ + delay_us = timer_get_us() - priv->last_transaction_us; + if (delay_us < pdata->deactivate_delay_us) + udelay(pdata->deactivate_delay_us - delay_us); + } + + clrbits_le32(&priv->regs->cs_reg, SPI_SLAVE_SIG_INACT); + debug("Activate CS, bus '%s'\n", bus->name); + priv->skip_preamble = priv->mode & SPI_PREAMBLE; +} + +All we have really done here is change the pointers and print the device name +instead of the bus number. Other local static functions can be treated in +the same way. + + +16. Set up the per-child data and child pre-probe function + +To minimise the pain and complexity of the SPI subsystem while the driver +model change-over is in place, struct spi_slave is used to reference a +SPI bus slave, even though that slave is actually a struct udevice. In fact +struct spi_slave is the device's child data. We need to make sure this space +is available. It is possible to allocate more space that struct spi_slave +needs, but this is the minimum. + +U_BOOT_DRIVER(exynos_spi) = { +... + .per_child_auto_alloc_size = sizeof(struct spi_slave), +} + + +17. Optional: Set up cs_info() if you want it + +Sometimes it is useful to know whether a SPI chip select is valid, but this +is not obvious from outside the driver. In this case you can provide a +method for cs_info() to deal with this. If you don't provide it, then the +device tree will be used to determine what chip selects are valid. + +Return -ENODEV if the supplied chip select is invalid, or 0 if it is valid. +If you don't provide the cs_info() method, -ENODEV is assumed for all +chip selects that do not appear in the device tree. + + +18. Test it + +Now that you have the code written and it compiles, try testing it using +the 'sf test' command. You may need to enable CONFIG_CMD_SF_TEST for your +board. + + +19. Prepare patches and send them to the mailing lists + +You can use 'tools/patman/patman' to prepare, check and send patches for +your work. See the README for details. |