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Subject: Re: [PATCH] mmc: meson-gx: do not use memcpy_to/fromio for
 dram-access-quirk
To:     Ulf Hansson <ulf.hansson@linaro.org>
Cc:     linux-mmc <linux-mmc@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        "open list:ARM/Amlogic Meson..." <linux-amlogic@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Christian Hewitt <christianshewitt@gmail.com>,
        Martin Blumenstingl <martin.blumenstingl@googlemail.com>
References: <20210913080504.832521-1-narmstrong@baylibre.com>
 <CAPDyKFqLvnAOAmk3PeNiBzwXTgwvG+zEO1b_pJNzSuUZ3Zamxg@mail.gmail.com>
From:   Neil Armstrong <narmstrong@baylibre.com>
Organization: Baylibre
Message-ID: <07dcfe81-c7cd-69d6-3f22-9f58cc2e1fb0@baylibre.com>
Date:   Thu, 23 Sep 2021 15:14:49 +0200
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Hi,

On 23/09/2021 12:51, Ulf Hansson wrote:
> On Mon, 13 Sept 2021 at 10:05, Neil Armstrong <narmstrong@baylibre.com> wrote:
>>
>> The memory at the end of the controller only accepts 32bit read/write
>> accesses, but the arm64 memcpy_to/fromio implementation only uses 64bit
>> (which will be split into two 32bit access) and 8bit leading to incomplete
>> copies to/from this memory when the buffer is not multiple of 8bytes.
>>
>> Add a local copy using writel/readl accesses to make sure we use the right
>> memory access width.
>>
>> The switch to memcpy_to/fromio was done because of 285133040e6c
>> ("arm64: Import latest memcpy()/memmove() implementation"), but using memcpy
>> worked before since it mainly used 32bit memory acceses.
>>
>> Fixes: 103a5348c22c ("mmc: meson-gx: use memcpy_to/fromio for dram-access-quirk")
>> Reported-by: Christian Hewitt <christianshewitt@gmail.com>
>> Suggested-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
>> Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
>> ---
>>  drivers/mmc/host/meson-gx-mmc.c | 49 +++++++++++++++++++++++----------
>>  1 file changed, 35 insertions(+), 14 deletions(-)
>>
>> diff --git a/drivers/mmc/host/meson-gx-mmc.c b/drivers/mmc/host/meson-gx-mmc.c
>> index 3f28eb4d17fe..08c0ff0bfa8b 100644
>> --- a/drivers/mmc/host/meson-gx-mmc.c
>> +++ b/drivers/mmc/host/meson-gx-mmc.c
>> @@ -746,7 +746,7 @@ static void meson_mmc_desc_chain_transfer(struct mmc_host *mmc, u32 cmd_cfg)
>>         writel(start, host->regs + SD_EMMC_START);
>>  }
>>
>> -/* local sg copy to buffer version with _to/fromio usage for dram_access_quirk */
>> +/* local sg copy for dram_access_quirk */
>>  static void meson_mmc_copy_buffer(struct meson_host *host, struct mmc_data *data,
>>                                   size_t buflen, bool to_buffer)
>>  {
>> @@ -764,21 +764,34 @@ static void meson_mmc_copy_buffer(struct meson_host *host, struct mmc_data *data
>>         sg_miter_start(&miter, sgl, nents, sg_flags);
>>
>>         while ((offset < buflen) && sg_miter_next(&miter)) {
>> -               unsigned int len;
>> +               unsigned int buf_offset = 0;
>> +               unsigned int len, left;
>> +               u32 *buf = miter.addr;
>> +
>> +               if (((unsigned long int)miter.addr % 4))
>> +                       dev_err(host->dev, "non word aligned sg");
> 
> This looks weird. You print an error message, but continue to process
> data? If this is a case you can't handle, perhaps you should propagate
> an error code instead?
> 
> Additionally, you may want to use the IS_ALIGNED() macro.
> 
>>
>>                 len = min(miter.length, buflen - offset);
>>
>> -               /* When dram_access_quirk, the bounce buffer is a iomem mapping */
>> -               if (host->dram_access_quirk) {
>> -                       if (to_buffer)
>> -                               memcpy_toio(host->bounce_iomem_buf + offset, miter.addr, len);
>> -                       else
>> -                               memcpy_fromio(miter.addr, host->bounce_iomem_buf + offset, len);
>> +               if ((len % 4))
>> +                       dev_err(host->dev, "non word multiple sg");
> 
> Again, a dev_err() doesn't seem like the right thing to do. If you
> can't handle this, please return an error code instead.
> 
> Perhaps returning an error code isn't convenient at this point. An
> option could then be to pre-validate the sglist at the time of
> starting the request. We have other host drivers doing this, have a
> look at drivers/mmc/host/mmci*, for example.

Yep pre-validating the data at the request callback seems the best solution,

Thanks,
Neil

> 
>> +
>> +               left = len;
>> +
>> +               if (to_buffer) {
>> +                       do {
>> +                               writel(*buf++, host->bounce_iomem_buf + offset + buf_offset);
>> +
>> +                               buf_offset += 4;
>> +                               left -= 4;
>> +                       } while (left);
>>                 } else {
>> -                       if (to_buffer)
>> -                               memcpy(host->bounce_buf + offset, miter.addr, len);
>> -                       else
>> -                               memcpy(miter.addr, host->bounce_buf + offset, len);
>> +                       do {
>> +                               *buf++ = readl(host->bounce_iomem_buf + offset + buf_offset);
>> +
>> +                               buf_offset += 4;
>> +                               left -= 4;
>> +                       } while (left);
>>                 }
>>
>>                 offset += len;
>> @@ -830,7 +843,11 @@ static void meson_mmc_start_cmd(struct mmc_host *mmc, struct mmc_command *cmd)
>>                 if (data->flags & MMC_DATA_WRITE) {
>>                         cmd_cfg |= CMD_CFG_DATA_WR;
>>                         WARN_ON(xfer_bytes > host->bounce_buf_size);
>> -                       meson_mmc_copy_buffer(host, data, xfer_bytes, true);
>> +                       if (host->dram_access_quirk)
>> +                               meson_mmc_copy_buffer(host, data, xfer_bytes, true);
>> +                       else
>> +                               sg_copy_to_buffer(data->sg, data->sg_len,
>> +                                                 host->bounce_buf, xfer_bytes);
>>                         dma_wmb();
>>                 }
>>
>> @@ -999,7 +1016,11 @@ static irqreturn_t meson_mmc_irq_thread(int irq, void *dev_id)
>>         if (meson_mmc_bounce_buf_read(data)) {
>>                 xfer_bytes = data->blksz * data->blocks;
>>                 WARN_ON(xfer_bytes > host->bounce_buf_size);
>> -               meson_mmc_copy_buffer(host, data, xfer_bytes, false);
>> +               if (host->dram_access_quirk)
>> +                       meson_mmc_copy_buffer(host, data, xfer_bytes, false);
>> +               else
>> +                       sg_copy_from_buffer(data->sg, data->sg_len,
>> +                                           host->bounce_buf, xfer_bytes);
>>         }
>>
>>         next_cmd = meson_mmc_get_next_command(cmd);
>> --
>> 2.25.1
>>
> 
> Kind regards
> Uffe
>