[PATCH] mmc: meson: Add driver for the SD/MMC host found on Amlogic MesonX SoCs

[Daniel Drake]

Hi Carlo,

On Mon, Jun 8, 2015 at 11:09 AM, Carlo Caione <carlo at caione.org> wrote:
> From: Carlo Caione <carlo at endlessm.com>
>
> Add a driver for the SD/MMC host found on the Amlogic MesonX SoCs. It
> is an MMC controller which provides an interface between the
> application processor and various memory cards. It supports the SD
> specification v2.0 and the eMMC specification v4.41. It also supports
> SDSC, SDHC and SDXC memory card default speed.

Nice work, thanks for this!

> This patch adds also the bindinding documentation.

"binding" typo

> +static void meson_mmc_request(struct mmc_host *mmc, struct mmc_request *mrq)
> +{
> +       struct meson_mmc_host *host = mmc_priv(mmc);
> +       struct mmc_command *cmd = mrq->cmd;
> +       struct mmc_data *data = mrq->data;
> +       unsigned long flags;
> +
> +       spin_lock_irqsave(&host->lock, flags);
> +
> +       if (host->state != STATE_IDLE) {
> +               dev_dbg(mmc_dev(mmc), "%s() rejected, state %u\n",
> +                       __func__, host->state);
> +               mrq->cmd->error = -EAGAIN;
> +               spin_unlock_irqrestore(&host->lock, flags);
> +               mmc_request_done(mmc, mrq);
> +               return;
> +       }
> +
> +       if (host->ferror) {
> +               cmd->error = host->ferror;
> +               spin_unlock_irqrestore(&host->lock, flags);
> +               mmc_request_done(mmc, mrq);
> +               return;
> +       }
> +
> +       dev_dbg(mmc_dev(mmc), "CMD%d(%08x) arg %x len %d flags %08x\n",
> +               cmd->opcode & 0x3f, cmd->opcode, cmd->arg,
> +               mrq->data ? mrq->data->blksz * mrq->data->blocks : 0,
> +               mrq->cmd->flags);
> +
> +       /* Filter out CMD 5/52/53 */
> +       if (cmd->opcode == SD_IO_SEND_OP_COND ||
> +           cmd->opcode == SD_IO_RW_DIRECT ||
> +           cmd->opcode == SD_IO_RW_EXTENDED) {
> +               dev_dbg(mmc_dev(host->mmc), "CMD%d not supported\n", cmd->opcode);
> +               cmd->error = -EINVAL;
> +               spin_unlock_irqrestore(&host->lock, flags);
> +               mmc_request_done(mmc, mrq);
> +               return;
> +       }
> +
> +       host->state = STATE_REQUEST;
> +
> +       if (data) {
> +               meson_mmc_map_dma(host, data, data->flags);
> +               writel(host->sg_dma, host->base + SDIO_ADDR);

As the sg_dma buffer is constant, can you do this register write just
once at probe time? I wonder if we really need to do it on each
request.

Or, going deeper, I wonder if we can avoid this bounce buffer
entirely. Can you try setting mmc->max_segs to 1 then passing the
single data segment directly to the hardware with
   writel(sg_dma_address(data->sg), host->base + SDIO_ADDR)

If that turns out to be more complicated then it sounds, then feel
free to push it off to a later driver revision.

Thanks!
Daniel