On Thu, 22 Nov 2007 10:41:43 +0000
Dean Jenkins <[EMAIL PROTECTED]> wrote:
> Hi Pierre,
>
> I've been checking my SDIO CMD53 data transfers and I notice the
> following:
>
> block size = 256 bytes for my SDIO card.
>
> transfers of 256 bytes uses byte mode ( I expected block mode )
> transfers of 512 bytes uses block mode ( because blocks = 2 )
>
> From the SD spec a single block transfer seems to be valid.
>
Both are valid, which is the source of the problem. The API was designed under
the assumption that hardware actually followed the register interface and
didn't distinguish between byte and block transfers. Unfortunately, it seems to
be quite common that they do. Your situation is a problematic corner case.
>
> If it is a bug then I suggest the sdio_io_rw_ext_helper() in sdio_io.c
> be able to select byte mode by setting blocks to 0 and then blocks can
> be set to 1 to select block mode for a single block.
>
I'm afraid I don't follow. Do you want to add another parameter? Even if you
do, sdio_io_rw_ext_helper() is an internal API. Changing it won't make things
better for the function drivers.
>
> Technically, there is a bug in sdio_io_rw_ext_helper() in sdio_io.c
>
> 211 while (remainder > func->cur_blksize) {
>
> should be, = missing
>
> 211 while (remainder >= func->cur_blksize) {
>
Unless some hardware is quirky in the opposite way and needs to be able to do
byte transfer of 256 bytes. Proper cards won't care either way, but as you can
see, we can't support both types of buggy cards.
> however the resulting call to mmc_io_rw_extended() is the same as blocks
> = 1 for both the "block mode" while loop (with the "fix") and the "byte
> mode" while loop (without the "fix"). The "byte mode" while loop has a
> hard coded value of 1 for the blocks parameter. So the bug is masked. As
> I said above, I think the "byte mode" should use a value of 0 for the
> blocks parameter.
>
Ah. mmc_io_rw_extended() is indeed broken in that it can't do single block
requests. That should be fixed.
However, it still won't affect what your function driver can do as
mmc_io_rw_extended() is a bunch of layers down.
I guess I'll have to consider adding a more low-level API. The big problem with
such a call would be that it can fail requests because the host or card cannot
satisfy them. So a function driver using such an API would have to use a much
more defensive programming (which can incur a performance hit).
Rgds
--
-- Pierre Ossman
Linux kernel, MMC maintainer http://www.kernel.org
PulseAudio, core developer http://pulseaudio.org
rdesktop, core developer http://www.rdesktop.org
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