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

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Date:   Wed, 15 May 2019 23:18:17 +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 Wed, May 15, 2019 at 2:45 PM Neil Armstrong <narmstrong@...libre.com> wrote:
>
> On 14/05/2019 19:58, Martin Blumenstingl wrote:
> > 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?
>
> We still need the physical bounce buffer address since we write in the registers,
so writing bounce_dma_addr to SD_EMMC_CMD_DAT is needed to make it work?

> and we need the logical address to memcpy() in the buffer.
as far as I understand that is what we use the "bounce_buf" member
for, but I don't see why we need "bounce_dma_addr"

> >
> >> +       } 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)
>
> It can be allocated, it's only useless. I can skip it but I don't want
> to break any logic in the driver.
I wasn't clear in my last email, I meant this error case:
  err_bounce_buf:
    dma_free_coherent(host->dev, host->bounce_buf_size, ...
when host->ddr_access_quirk is true then you skip the
dma_alloc_coherent call for bounce_buf


Martin