Re: [PATCH v2 14/14] mmc: mmci: Add Qcom specific pio_read function.

[Srinivas Kandagatla]

Hi Linus W,

On 23/05/14 10:31, Linus Walleij wrote:
> static int mmci_qcom_pio_read(struct mmci_host *host, char *buffer,
>                          unsigned int remain)
> {
>         u32 *ptr = (u32*) buffer;
>         unsigned int count = 0;
>         unsigned int words;
>         unsigned int fifo_size = host->variant->fifosize;
>
>         words = DIV_ROUND_UP(remain, 4);
>         while (readl(host->base + MMCISTATUS) & MCI_RXDATAAVLBL) {
>                 *ptr = readl(host->base + MMCIFIFO + (count % fifo_size));
>                 ptr++;
>                 count += 4;
>                 remain--;
>                 if (!remain)
>                         break;
>         }
>         return count;
> }
>
> I guess you will run into additional problems when you come to doing
> SDIO. This function can return*more*  bytes than asked for, as it rounds
> up. It won't happen with MMC/SD transfers since these are always
> divisible by 8, but it*will*  happen on SDIO!
That's a good point,

Qualcomm will need SDIO support in future, so I have slightly modified 
the  code to address this. Other thing I tried was to fit in this in 
mmci_pio_read, It became very ugly, as the FIFOCNT register behaviour is 
totally different and there is no way to tell how many bytes are ready 
to be consumed. So finally I think having a separate pio read for 
qualcomm looks much neater.

final mmci_qcom_pio_read looks like:


static int mmci_qcom_pio_read(struct mmci_host *host, char *buffer,
            unsigned int remain)
{
    u32 *ptr = (u32*) buffer;
    unsigned int count = 0;
    unsigned int words, bytes;
    unsigned int fifo_size = host->variant->fifosize;

    words = remain >> 2;
    bytes = remain % 4;
    /* read full words followed by leftover bytes */
    if (words) {
        while (readl(host->base + MMCISTATUS) & MCI_RXDATAAVLBL) {
            *ptr = readl(host->base + MMCIFIFO + (count % fifo_size));
            ptr++;
            count += 4;
            words--;
            if (!words)
                break;
         }
    }

    /* read leftover bytes */
    if (unlikely(bytes)) {
        unsigned char buf[4];
        if (readl(host->base + MMCISTATUS) & MCI_RXDATAAVLBL) {
            *buf = readl(host->base + MMCIFIFO + (count % fifo_size));
            memcpy(ptr, buf, bytes);
             count += bytes;
        }
    }

    return count;
}

Thanks,
srini

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/