On Tue, 21 Jun 2011, Per Forlin wrote: > On 21 June 2011 07:41, Kishore Kadiyala <kishorek.kadiyala@xxxxxxxxx> 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 > pre_req. > * 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. Nicolas
