Re: [RFC] mmc: dw_mmc: Fix the max_blk_count in IDMAC

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2012/2/23 Seungwon Jeon <tgih.jun@xxxxxxxxxxx>:
> Hi all,
>
> Even though 1MB is reserved for descriptor table in IDMAC,
> the dw_mmc host driver is allowed to receive only maximum
> 128KB block length in one request. This is caused by setting
> improper max_blk_count. It needs to be e adjusted so that
> descriptor table is used fully.
>
> It is found that the performance is improved with the increased the
> max_blk_count. In my case, there is 82%(6%) improvement in sequential
> write(read). Is there anybody who knows the reason about the old setting?
>
> Best regards,
> Seungwon Jeon.
>
> Signed-off-by: Seungwon Jeon <tgih.jun@xxxxxxxxxxx>
> ---
>  drivers/mmc/host/dw_mmc.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index bf3c9b4..af2b901 100644
> --- a/drivers/mmc/host/dw_mmc.c
> +++ b/drivers/mmc/host/dw_mmc.c
> @@ -1804,9 +1804,9 @@ static int __init dw_mci_init_slot(struct dw_mci *host, unsigned int id)
>  #ifdef CONFIG_MMC_DW_IDMAC
>                mmc->max_segs = host->ring_size;
>                mmc->max_blk_size = 65536;
> -               mmc->max_blk_count = host->ring_size;
>                mmc->max_seg_size = 0x1000;
> -               mmc->max_req_size = mmc->max_seg_size * mmc->max_blk_count;
> +               mmc->max_req_size = mmc->max_seg_size * host->ring_size;
> +               mmc->max_blk_count = mmc->max_req_size / 512;

I am not sure this is correct, it seems like most drivers calculate
max_req_size like this:

mmc->max_req_size = mmc->max_blk_size * mmc->max_blk_count;

And indeed in the external DMA case dw_mmc does that too.

It should probably be safe to set max_seg_size to max_req_size too.

>  #else
>                mmc->max_segs = 64;
>                mmc->max_blk_size = 65536; /* BLKSIZ is 16 bits */
> --
> 1.7.0.4
>
>
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