[PATCH] mmc: mxs-mmc: add support for pre_req and post_req

[Per Forlin]

On 21 April 2011 11:47, Per Forlin <per.forlin at linaro.org> wrote:
> On 21 April 2011 11:11, Shawn Guo <shawn.guo at freescale.com> wrote:
>> On Thu, Apr 21, 2011 at 10:46:18AM +0200, Per Forlin wrote:
>>> On 21 April 2011 08:29, Shawn Guo <shawn.guo at freescale.com> wrote:
>>> > On Wed, Apr 20, 2011 at 05:30:22PM +0200, Per Forlin wrote:
>>> > [...]
>>> >> Remove dma_map and dma_unmap from your host driver and run the tests
>>> >> (obviously nonblocking and blocking will have the same results). If
>>> >> there is still no performance gain the cache penalty is very small on
>>> >> your platform and therefore nonblocking doesn't improve things much.
>>> >> Please let me know the result.
>>> >>
>>> > Sorry, I could not understand.  What's the point to run the test when
>>> > the driver is even broken.  The removal of  dma_map_sg and
>>> > dma_unmap_sg makes mxs-mmc host driver broken.
>>> The point is only to get a measurement of the cost of handling
>>> dma_map_sg and dma_unmap_sg, this is the maximum time mmc nonblocking
>>> can save.
>>> The nonblocking mmc_test should save the total time of dma_map_sg and
>>> dma_unmap_sg, if the pre_req and post_req hooks are implemented
>>> correctly.
>>> Running without dma_map_sg and dma_unmap_sg will confirm if the
>>> pre_req and post_req hooks are implemented correctly.
>>>
>> With dma_map_sg and dma_unmap_sg removed, the mmc_test gave very low
>> numbers, though blocking and non-blocking numbers are same.  Is it
>> an indication that pre_req and post_req hooks are not implemented
>> correctly?
> I think you could get the same numbers for the nonblocking with
> dma_map and dma_unmap in place.
>
>>  If yes, can you please help to catch the mistakes?
> I will take a look.
>
I found something:
static void mxs_mmc_request(struct mmc_host *mmc, struct mmc_request *mrq)
{
	struct mxs_mmc_host *host = mmc_priv(mmc);

	WARN_ON(host->mrq != NULL);
	host->mrq = mrq;
	mxs_mmc_start_cmd(host, mrq->cmd);
}

This is the execution flow:
pre_req()
mxs_mmc_request()
post_req()
wait_for_completion()
pre_req()

mxs_mmc_request() returns before the prepared value is used
post_req() will run dma_unmap and set the cookie to 0, this mean in
your case dma_unmap_sg will be called twice.
You need to store away the prepared data in mxs_mmc_request().
Look at my patch for mmci, function mmci_get_next_data. That function
deals with this issue.

I didn't see this issue when I only looked at the patch since no
changes are made in the request-function.

>> --
>> Regards,
>> Shawn
Regards,
Per