linux-kernel - Re: [PATCH 1/4] mmc: sdhci-esdhc: Add SDHCI_QUIRK_32BIT_DMA

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Message-ID: <CAK8P3a3H5b+aPXjv6HT2TBTvZnU2Xy-Gg2MEMAC66MgpqQd9cg@mail.gmail.com>
Date:   Thu, 4 May 2017 11:37:58 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Benoît Thébaudeau <benoit@...stem.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mmc@...r.kernel.org, Ulf Hansson <ulf.hansson@...aro.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Fabio Estevam <fabio.estevam@....com>,
        Wolfram Sang <wsa@...-dreams.de>
Subject: Re: [PATCH 1/4] mmc: sdhci-esdhc: Add SDHCI_QUIRK_32BIT_DMA_ADDR

On Thu, May 4, 2017 at 11:00 AM, Benoît Thébaudeau <benoit@...stem.com> wrote:
> On 04/05/2017 10:47, Arnd Bergmann wrote:
>> On Wed, May 3, 2017 at 12:05 PM, Benoît Thébaudeau <benoit@...stem.com> wrote:
>>> The eSDHC can only DMA from 32-bit-aligned addresses.
>>>
>>> This fixes the following test cases of mmc_test:
>>>   11:   Badly aligned write
>>>   12:   Badly aligned read
>>>   13:   Badly aligned multi-block write
>>>   14:   Badly aligned multi-block read
>>>
>>> Signed-off-by: Benoît Thébaudeau <benoit@...stem.com>
>>
>> Is this the right description? I thought that SDHCI_QUIRK_32BIT_DMA_ADDR
>> was for devices that cannot address high memory above 0xffffffff, rather than
>> requiring a specific alignment.
>>
>> If this is indeed an address range problem rather than an alignment problem,
>> are you sure it is the SD controller that is wrong here, rather than having a
>> 64-bit DMA capable  SDHCI connected to a 32-bit parent bus? In the
>> latter case, the dma-ranges property in the parent bus should limit
>> the addressing, not the device.
>
> No, this is the right description. This quirk really is about alignment, and not
> about address range. See:
>
> drivers/mmc/host/sdhci.h:
>>---
> /* Controller can only DMA from 32-bit aligned addresses */
> #define SDHCI_QUIRK_32BIT_DMA_ADDR                      (1<<7)
> <---
>
> drivers/mmc/host/sdhci.c @ sdhci_prepare_data():
>>---
>                 offset_mask = 0;
> [...]
>                         if (host->quirks & SDHCI_QUIRK_32BIT_DMA_ADDR)
>                                 offset_mask = 3;

Ok, thanks for the clarification. I guess I should have checked this myself
first.

       Arnd