On Tue, 21 Jun 2011, Per Forlin wrote:

On 21 June 2011 07:41, Kishore Kadiyala [off-list ref] wrote:

quoted

<snip>

quoted

+
+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