linux-kernel - Re: [PATCH 2/3] mmc: meson-gx: add ddr-access-quirk

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Date:   Tue, 14 May 2019 19:58:00 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Neil Armstrong <narmstrong@...libre.com>
Cc:     ulf.hansson@...aro.org, khilman@...libre.com,
        baylibre-upstreaming@...ups.io, linux-mmc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/3] mmc: meson-gx: add ddr-access-quirk

Hi Neil,

On Mon, May 13, 2019 at 11:16 AM Neil Armstrong <narmstrong@...libre.com> wrote:
[...]
> @@ -1158,15 +1183,27 @@ static int meson_mmc_probe(struct platform_device *pdev)
>          */
>         mmc->caps2 &= ~MMC_CAP2_HS400;
>
> -       /* data bounce buffer */
> -       host->bounce_buf_size = mmc->max_req_size;
> -       host->bounce_buf =
> -               dma_alloc_coherent(host->dev, host->bounce_buf_size,
> -                                  &host->bounce_dma_addr, GFP_KERNEL);
> -       if (host->bounce_buf == NULL) {
> -               dev_err(host->dev, "Unable to map allocate DMA bounce buffer.\n");
> -               ret = -ENOMEM;
> -               goto err_free_irq;
> +       if (host->ddr_access_quirk) {
> +               /*
> +                * The MMC Controller embeds 1,5KiB of internal SRAM
> +                * that can be used to be used as bounce buffer.
> +                * In the case of the G12A SDIO controller, use these
> +                * instead of the DDR memory
> +                */
> +               host->bounce_buf_size = SD_EMMC_SRAM_DATA_BUF_LEN;
> +               host->bounce_buf = host->regs + SD_EMMC_SRAM_DATA_BUF_OFF;
> +               host->bounce_dma_addr = res->start + SD_EMMC_SRAM_DATA_BUF_OFF;
I'm curious: why do you need to set bounce_dma_addr in this case?

> +       } else {
> +               /* data bounce buffer */
> +               host->bounce_buf_size = mmc->max_req_size;
> +               host->bounce_buf =
> +                       dma_alloc_coherent(host->dev, host->bounce_buf_size,
> +                                          &host->bounce_dma_addr, GFP_KERNEL);
> +               if (host->bounce_buf == NULL) {
> +                       dev_err(host->dev, "Unable to map allocate DMA bounce buffer.\n");
> +                       ret = -ENOMEM;
> +                       goto err_free_irq;
> +               }
>         }
>
>         host->descs = dma_alloc_coherent(host->dev, SD_EMMC_DESC_BUF_LEN,
if host->descs cannot be allocated then you need to conditionally skip
dma_free_coherent for the bounce buffer in the goto err_bounce_buf
case a few lines below (just like you did in meson_mmc_remove)


Martin