linux-kernel - Re: [PATCH V3 1/3] mmc: sdhci: add support for using external DMA devices

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Date:   Mon, 3 Dec 2018 19:28:03 +0530
From:   Faiz Abbas <faiz_abbas@...com>
To:     Chunyan Zhang <zhang.chunyan@...aro.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Adrian Hunter <adrian.hunter@...el.com>
CC:     <linux-mmc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>, Mark Brown <broonie@...nel.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        Sekhar Nori <nsekhar@...com>,
        Chunyan Zhang <zhang.lyra@...il.com>
Subject: Re: [PATCH V3 1/3] mmc: sdhci: add support for using external DMA
 devices

Hi,

On 03/12/18 5:45 PM, Faiz Abbas wrote:
> Hi,
> 
>> +static void sdhci_external_dma_prepare_data(struct sdhci_host *host,
>> +					    struct mmc_command *cmd)
>> +{
> 
> Please add a condition for data == NULL here. This was already pointed
> out by Adrian in v2.
> 
> My test with an am335x-evm failed with these patches. Looks like the
> very first SDIO commands failing.
> 
> https://pastebin.ubuntu.com/p/Y2RDjSKpgd/
> 
> Currently am335x-evm is using omap_hsmmc driver. I added the following
> patch to make it work with sdhci_omap.
> 
> https://pastebin.ubuntu.com/p/VTGrCbJxY3/
> 
> Will look deeper into this. Please ping if you need any more information.
> 

So I disabled DMA in the driver altogether and still got the same
messages on am335x-evm in PIO mode. Looks like something more is
required for it to be supported.

I instead shifted to a dra71-evm which supports both ADMA and external
DMA. Here is the log:

https://pastebin.ubuntu.com/p/mcJmgcjQsp/

The interface fundamentally works but it complains with the following error:

[3.111693] Failed to request TX DMA channel.


Thanks,
Faiz