From: Ulf Hansson <email@example.com>
To: Kishon Vijay Abraham I <firstname.lastname@example.org>,
Arnd Bergmann <email@example.com>,
Chunyan Zhang <firstname.lastname@example.org>
Cc: Adrian Hunter <email@example.com>,
Linux Kernel Mailing List <firstname.lastname@example.org>,
Mark Brown <email@example.com>, Sekhar Nori <firstname.lastname@example.org>,
Chunyan Zhang <email@example.com>
Subject: Re: [PATCH RFC 2/3] mmc: sdhci-omap: Add using external dma
Date: Mon, 19 Nov 2018 17:32:25 +0100 [thread overview]
Message-ID: <CAPDyKFpomN9KyX5u8C9-gBwBNm-sdfHwxbDVYD0hs73WFJR53A@mail.gmail.com> (raw)
On 9 November 2018 at 06:27, Kishon Vijay Abraham I <firstname.lastname@example.org> wrote:
> Hi Arnd,
> On 06/11/18 6:21 PM, Arnd Bergmann wrote:
>> On 11/5/18, Kishon Vijay Abraham I <email@example.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
>>> DMA shouldn't be unconditional.
>>> IMHO sdhci.c should see if the device supports ADMA or SDMA. If not it
>>> 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?
> Generally from our experiments we've found ADMA gives better throughput than
> DMA. I have to ascertain the actual reasons for that.
>> 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.
> I would agree that for newer dtbs. However if you consider omap_hsmmc, external
> DMA bindings are already added in dt. If we try to switch to sdhci-omap with
> the same bindings, systems with older dtbs will use external DMA and give
> lesser throughput.
I was under the impression that the internal DMA (for old versions) is
However, in the end this is a software policy decision of what to use.
I have no strong opinion, so feel free to pick what you think makes
Maybe Adrian also have some thoughts?
next prev parent reply other threads:[~2018-11-19 16:33 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
2018-11-07 3:00 ` Chunyan Zhang
2018-11-09 5:27 ` Kishon Vijay Abraham I
2018-11-19 16:32 ` Ulf Hansson [this message]
2018-11-05 3:16 ` [PATCH RFC 3/3] dt-bindings: sdhci-omap: Add example for using dmaengine Chunyan Zhang
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