On Tue, 21 Jun 2011, Per Forlin wrote:
On 21 June 2011 07:41, Kishore Kadiyala kishorek.kadiyala@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 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