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

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Date:   Wed, 15 May 2019 14:45:38 +0200
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.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

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,
and we need the logical address to memcpy() in the buffer.

> 
>> +       } 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.

> 
> 
> Martin
>