Hi Jaehoon,
On Thu, Apr 07, 2011 at 05:04:52PM +0900, Jaehoon Chung wrote:
[...]
> +static unsigned int dw_mci_pre_dma_transfer(struct dw_mci *host,
> + struct mmc_data *data, struct dw_mci_next *next)
> +{
> + unsigned int sg_len;
> +
> + BUG_ON(next && data->host_cookie);
> + BUG_ON(!next && data->host_cookie &&
> + data->host_cookie != host->next_data.cookie);
> +
> + if (!next && data->host_cookie &&
> + data->host_cookie != host->next_data.cookie) {
> + data->host_cookie = 0;
> + }
> +
I'm unsure if the 'if' statement makes any sense here, since the
exactly same conditions have been caught by the BUG_ON just above
it.
> + if (next ||
> + (!next && data->host_cookie != host->next_data.cookie)) {
> + sg_len = dma_map_sg(&host->pdev->dev, data->sg,
> + data->sg_len, ((data->flags & MMC_DATA_WRITE)
> + ? DMA_TO_DEVICE : DMA_FROM_DEVICE));
> + } else {
> + sg_len = host->next_data.sg_len;
> + host->next_data.sg_len = 0;
> + }
> +
> + if (sg_len == 0)
> + return -EINVAL;
> +
> + if (next) {
> + next->sg_len = sg_len;
> + data->host_cookie = ++next->cookie < 0 ? 1 : next->cookie;
> + } else
> + data->sg_len = sg_len;
> +
> + return sg_len;
> +}
> +
Function dw_mci_pre_dma_transfer() returns non-zero value anyway,
either -EINVAL or sg_len ...
[...]
> +static void dw_mci_pre_request(struct mmc_host *mmc, struct mmc_request *mrq,
> + bool is_first_req)
> +{
> + struct dw_mci_slot *slot = mmc_priv(mmc);
> + struct mmc_data *data = mrq->data;
> +
> + if (!data)
> + return;
> +
> + BUG_ON(mrq->data->host_cookie);
> +
> + if (slot->host->use_dma) {
> + if (dw_mci_pre_dma_transfer(slot->host, mrq->data,
> + &slot->host->next_data))
> + mrq->data->host_cookie = 0;
... while it steps back to old blocking way by setting
data->host_cookie 0 when dw_mci_pre_dma_transfer returns non-zero.
Per my understanding, it means the non-blocking optimization will
always get bypassed anyway, so I doubt the patch can really gain
performance improvement. Did you get the chance to measure?
--
Regards,
Shawn
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