linux-kernel - Re: [PATCH v2 1/3] mmc: sdhci: add support for using external DMA devices

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Date:   Thu, 29 Nov 2018 17:59:46 +0800
From:   Chunyan Zhang <zhang.lyra@...il.com>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Chunyan Zhang <zhang.chunyan@...aro.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-mmc@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>, Mark Brown <broonie@...nel.org>,
        kishon@...com, nsekhar@...com
Subject: Re: [PATCH v2 1/3] mmc: sdhci: add support for using external DMA devices

Hi Adrian,

On Thu, 29 Nov 2018 at 15:36, Adrian Hunter <adrian.hunter@...el.com> wrote:
>
> On 29/11/18 8:22 AM, Chunyan Zhang wrote:
> > On Tue, 20 Nov 2018 at 21:41, Adrian Hunter <adrian.hunter@...el.com> wrote:
> >>
> >> On 12/11/18 9:26 AM, Chunyan Zhang wrote:
> >>> Some standard SD host controllers can support both external dma
> >>> controllers as well as ADMA/SDMA in which the SD host controller
> >>> acts as DMA master. TI's omap controller is the case as an example.
> >>>
> >>> Currently the generic SDHCI code supports ADMA/SDMA integrated in
> >>> the host controller but does not have any support for external DMA
> >>> controllers implemented using dmaengine, meaning that custom code is
> >>> needed for any systems that use an external DMA controller with SDHCI.
> >>
> >> I still think you probably need to reset the DMA if there are transfer
> >> errors - perhaps you could comment on that.  Also there are some comments below.
> >
> > With regard to "transfer error", do you mean if
> > sdhci_external_dma_setup() failed?
>
> No, I mean any error interrupt that can leave the DMA uncompleted.  For
> SDHCI, resetting the data circuit cleans that up, but presumably something
> is needed for external DMA?

Yes, it should need a dmaengine_terminate_all().

How about adding that at here (I will wrap it up of course):
https://elixir.bootlin.com/linux/v4.19.5/source/drivers/mmc/host/sdhci.c#L2553

Is there somewhere else I'm missing?

Thanks,
Chunyan