[PATCH v6 02/11] omap_hsmmc: add support for pre_req and post_req
nicolas.pitre at linaro.org
Tue Jun 21 15:18:32 EDT 2011
On Tue, 21 Jun 2011, Per Forlin wrote:
> On 21 June 2011 07:41, Kishore Kadiyala <kishorek.kadiyala at gmail.com> wrote:
> > <snip>
> >> +
> >> +static void omap_hsmmc_pre_req(struct mmc_host *mmc, struct mmc_request *mrq,
> >> + bool is_first_req)
> > I don't see the usage of "is_first_req" below.
> > Is it required?
> It is not required. It is only an indication that this request is the
> first in a series of request. The host driver may do various
> optimisations based on this information. The first request in a series
> of jobs can't be prepared in parallel to the previous job. The host
> driver can do the following to minimise latency for the first job.
> * Preparing the cache while the MMC read/write cmd is being
> processed. In this case the pre_req could do nothing and the job is
> instead run in parallel to the read/write cmd being sent. If the
> is_first_req is false pre_req will run in parallel to an active
> transfer, in this case it is more efficient to prepare the request in
> * Run PIO mode instead of DMA
That is never going to be a good tradeoff. If the CPU is busy doing
PIO, it won't have a chance to prepare a subsequent request in parallel
to the first transfer.
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