dfu: fix some issues with reads/uploads

DFU read support appears to rely upon dfu->read_medium() updating the
passed-by-reference len parameter to indicate the remaining size
available for reading.

dfu_read_medium_mmc() never does this, and the implementation of
dfu_read_medium_nand() will only work if called just once; it hard-codes
the value to the total size of the NAND device irrespective of read
offset.

I believe that overloading dfu->read_medium() is confusing. As such,
this patch introduces a new function dfu->get_medium_size() which can
be used to explicitly find out the medium size, and nothing else.
dfu_read() is modified to use this function to set the initial value for
dfu->r_left, rather than attempting to use the side-effects of
dfu->read_medium() for this purpose.

Due to this change, dfu_read() must initially set dfu->b_left to 0, since
no data has been read.

dfu_read_buffer_fill() must also be modified not to adjust dfu->r_left
when simply copying data from dfu->i_buf_start to the upload request
buffer. r_left represents the amount of data left to be read from HW.
That value is not affected by the memcpy(), but only by calls to
dfu->read_medium().

After this change, I can read from either a 4MB or 1.5MB chunk of a 4MB
eMMC boot partion with CONFIG_SYS_DFU_DATA_BUF_SIZE==1MB. Without this
change, attempting to do that would result in DFU read returning no data
at all due to r_left never being set.

Signed-off-by: Stephen Warren <swarren@nvidia.com>

1 files changed, 6 insertions, 5 deletions

diff --git a/drivers/dfu/dfu_ram.c b/drivers/dfu/dfu_ram.c
index 335a8e1..b6c6e60 100644
--- a/drivers/dfu/dfu_ram.c
+++ b/drivers/dfu/dfu_ram.c
@@ -41,14 +41,14 @@ static int dfu_write_medium_ram(struct dfu_entity *dfu, u64 offset,
 	return dfu_transfer_medium_ram(DFU_OP_WRITE, dfu, offset, buf, len);
 }
 
+long dfu_get_medium_size_ram(struct dfu_entity *dfu)
+{
+	return dfu->data.ram.size;
+}
+
 static int dfu_read_medium_ram(struct dfu_entity *dfu, u64 offset,
 			       void *buf, long *len)
 {
-	if (!*len) {
-		*len = dfu->data.ram.size;
-		return 0;
-	}
-
 	return dfu_transfer_medium_ram(DFU_OP_READ, dfu, offset, buf, len);
 }
 
@@ -69,6 +69,7 @@ int dfu_fill_entity_ram(struct dfu_entity *dfu, char *s)
 	dfu->data.ram.size = simple_strtoul(s, &s, 16);
 
 	dfu->write_medium = dfu_write_medium_ram;
+	dfu->get_medium_size = dfu_get_medium_size_ram;
 	dfu->read_medium = dfu_read_medium_ram;
 
 	dfu->inited = 0;