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SubjectRe: [PATCH 2/3] mmc: meson-gx: add ddr-access-quirk
Hi Neil,

On Wed, May 15, 2019 at 2:45 PM Neil Armstrong <narmstrong@baylibre.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@baylibre.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

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