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

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Date:   Thu, 16 May 2019 11:09:55 +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 15/05/2019 23:18, Martin Blumenstingl wrote:
> 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"

Sorry I don't understand these questions, I haven't changed the
bounce buffer behavior here, I only make it use a local SRAM buffer
instead of an dma_alloc_coherent() allocated buffer.

Having bounce_buf_size/bounce_buf/bounce_dma_addr is still necessary like
an allocated 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.
> 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

Oh, ok, yes, I'll add it.

Neil

> 
> 
> Martin
>