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From: Arnd Bergmann <arnd@arndb.de>
To: Kishon Vijay Abraham I <kishon@ti.com>
Cc: Chunyan Zhang <zhang.chunyan@linaro.org>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Adrian Hunter <adrian.hunter@intel.com>,
	linux-mmc@vger.kernel.org, linux-kernel@vger.kernel.org,
	Mark Brown <broonie@kernel.org>, Sekhar Nori <nsekhar@ti.com>,
	Chunyan Zhang <zhang.lyra@gmail.com>
Subject: Re: [PATCH RFC 2/3] mmc: sdhci-omap: Add using external dma
Date: Tue, 6 Nov 2018 13:51:17 +0100	[thread overview]
Message-ID: <CAK8P3a2X4tbx_R-5VgfApF-UPmJ_XuzH3hO_uVAfffC6h8WrJw@mail.gmail.com> (raw)
In-Reply-To: <be0a18e8-8ee6-4d4e-6dcc-6ba6e39033c9@ti.com>

On 11/5/18, Kishon Vijay Abraham I <kishon@ti.com> wrote:
> On 05/11/18 8:46 AM, Chunyan Zhang wrote:
>>
>> +	sdhci_switch_extdma(host, true);
>
> A number of devices using sdhci-omap supports ADMA. So switching to
> external
> DMA shouldn't be unconditional.
>
> IMHO sdhci.c should see if the device supports ADMA or SDMA. If not it
> should
> try switching to external DMA and if external DMA too is not supported, it
> should use PIO.

What's the reasoning for preferring ADMA/SDMA over external DMA if
both are supported?

I'd expect that if the external DMA for some reason is worse than
ADMA, we just wouldn't list it in the DT at all, but if it's listed and
ADMA also works, then the driver should try to use it before falling
back to ADMA.

       Arnd

  reply	other threads:[~2018-11-06 12:51 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-05  3:16 [PATCH RFC 0/3] Add support for using external dma in SDHCI Chunyan Zhang
2018-11-05  3:16 ` [PATCH RFC 1/3] mmc: sdhci: add support for using external DMA devices Chunyan Zhang
2018-11-06 11:16   ` Arnd Bergmann
2018-11-07  2:56     ` Chunyan Zhang
2018-11-07 14:13   ` Adrian Hunter
2018-11-05  3:16 ` [PATCH RFC 2/3] mmc: sdhci-omap: Add using external dma Chunyan Zhang
2018-11-05  4:25   ` Kishon Vijay Abraham I
2018-11-06 12:51     ` Arnd Bergmann [this message]
2018-11-07  3:00       ` Chunyan Zhang
2018-11-09  5:27       ` Kishon Vijay Abraham I
2018-11-19 16:32         ` Ulf Hansson
2018-11-05  3:16 ` [PATCH RFC 3/3] dt-bindings: sdhci-omap: Add example for using dmaengine Chunyan Zhang

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