Re: [PATCH v7 01/11] mmc: add non-blocking mmc request function

["S, Venkatraman" <svenkatr@ti.com>]

On Wed, Jun 22, 2011 at 2:15 PM, Per Forlin <per.forlin@linaro.org> wrote:
> On 22 June 2011 09:42, Venkatraman S <svenkatr@ti.com> wrote:
>> On Wed, Jun 22, 2011 at 5:08 AM, Per Forlin <per.forlin@linaro.org> wrote:
>>> Previously there has only been one function mmc_wait_for_req()
>>> to start and wait for a request. This patch adds
>>>  * mmc_start_req() - starts a request wihtout waiting
>>>   If there is on ongoing request wait for completion
>>>   of that request and start the new one and return.
>>>   Does not wait for the new command to complete.
>>>
>>> This patch also adds new function members in struct mmc_host_ops
>>> only called from core.c
>>>  * pre_req - asks the host driver to prepare for the next job
>>>  * post_req - asks the host driver to clean up after a completed job
>>>
>>> The intention is to use pre_req() and post_req() to do cache maintenance
>>> while a request is active. pre_req() can be called while a request is active
>>> to minimize latency to start next job. post_req() can be used after the next
>>> job is started to clean up the request. This will minimize the host driver
>>> request end latency. post_req() is typically used before ending the block
>>> request and handing over the buffer to the block layer.
>>>
>>> Add a host-private member in mmc_data to be used by
>>> pre_req to mark the data. The host driver will then
>>> check this mark to see if the data is prepared or not.
>>>
>>> Signed-off-by: Per Forlin <per.forlin@linaro.org>
>>> ---
>>>  drivers/mmc/core/core.c  |  110 +++++++++++++++++++++++++++++++++++++++++----
>>>  include/linux/mmc/core.h |    6 ++-
>>>  include/linux/mmc/host.h |   21 +++++++++
>>>  3 files changed, 126 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
>>> index 68091dd..c82fa3b 100644
>>> --- a/drivers/mmc/core/core.c
>>> +++ b/drivers/mmc/core/core.c
>>> @@ -198,9 +198,106 @@ mmc_start_request(struct mmc_host *host, struct mmc_request *mrq)
>>>
>>>  static void mmc_wait_done(struct mmc_request *mrq)
>>>  {
>>> -       complete(mrq->done_data);
>>> +       complete(&mrq->completion);
>>>  }
>>>
>>> +static void __mmc_start_req(struct mmc_host *host, struct mmc_request *mrq)
>>> +{
>>> +       init_completion(&mrq->completion);
>>> +       mrq->done = mmc_wait_done;
>>> +       mmc_start_request(host, mrq);
>>> +}
>>> +
>>> +static void mmc_wait_for_req_done(struct mmc_host *host,
>>> +                                 struct mmc_request *mrq)
>>> +{
>>> +       wait_for_completion(&mrq->completion);
>>> +}
>>> +
>>> +/**
>>> + *     mmc_pre_req - Prepare for a new request
>>> + *     @host: MMC host to prepare command
>>> + *     @mrq: MMC request to prepare for
>>> + *     @is_first_req: true if there is no previous started request
>>> + *                     that may run in parellel to this call, otherwise false
>>> + *
>>> + *     mmc_pre_req() is called in prior to mmc_start_req() to let
>>> + *     host prepare for the new request. Preparation of a request may be
>>> + *     performed while another request is running on the host.
>>> + */
>>> +static void mmc_pre_req(struct mmc_host *host, struct mmc_request *mrq,
>>> +                bool is_first_req)
>>> +{
>>> +       if (host->ops->pre_req)
>>> +               host->ops->pre_req(host, mrq, is_first_req);
>>> +}
>>> +
>>> +/**
>>> + *     mmc_post_req - Post process a completed request
>>> + *     @host: MMC host to post process command
>>> + *     @mrq: MMC request to post process for
>>> + *     @err: Error, if non zero, clean up any resources made in pre_req
>>> + *
>>> + *     Let the host post process a completed request. Post processing of
>>> + *     a request may be performed while another reuqest is running.
>>> + */
>>> +static void mmc_post_req(struct mmc_host *host, struct mmc_request *mrq,
>>> +                        int err)
>>> +{
>>> +       if (host->ops->post_req)
>>> +               host->ops->post_req(host, mrq, err);
>>> +}
>>> +
>>> +/**
>>> + *     mmc_start_req - start a non-blocking request
>>> + *     @host: MMC host to start command
>>> + *     @areq: async request to start
>>> + *     @error: out parameter returns 0 for success, otherwise non zero
>>> + *
>>> + *     Start a new MMC custom command request for a host.
>>> + *     If there is on ongoing async request wait for completion
>>> + *     of that request and start the new one and return.
>>> + *     Does not wait for the new request to complete.
>>> + *
>>> + *     Returns the completed async request, NULL in case of none completed.
>>> + */
>>> +struct mmc_async_req *mmc_start_req(struct mmc_host *host,
>>> +                                   struct mmc_async_req *areq, int *error)
>>> +{
>>> +       int err = 0;
>>> +       struct mmc_async_req *data = host->areq;
>>> +
>>> +       /* Prepare a new request */
>>> +       if (areq)
>>> +               mmc_pre_req(host, areq->mrq, !host->areq);
>>> +
>>> +       if (host->areq) {
>>> +               mmc_wait_for_req_done(host, host->areq->mrq);
>>> +               err = host->areq->err_check(host->card, host->areq);
>>> +               if (err) {
>>> +                       mmc_post_req(host, host->areq->mrq, 0);
>>> +                       if (areq)
>>> +                               mmc_post_req(host, areq->mrq, -EINVAL);
>>> +
>>> +                       host->areq = NULL;
>>> +                       goto out;
>> In this sequence, would the return value (data) have the previous areq ?
>> Is that intentional - doesn't seem to fit with the description.
> It will return the data that belongs to the completed request. The
> completed request will be the same as the previous request. The
> mmc_start_req will start a new request and return data for the
> completed request, if any.
>

I meant that in case of an error (err !=0), data is already assigned
to host->areq
and goto out returns 'data'. So my question was 'Does returning a non-null
pointer for a unsuccessful request doesn't fit with the description, does it ?'

Regards,
Venkat.