From: Ulf Hansson <firstname.lastname@example.org> To: Kishon Vijay Abraham I <email@example.com>, Arnd Bergmann <firstname.lastname@example.org>, Chunyan Zhang <email@example.com> Cc: Adrian Hunter <firstname.lastname@example.org>, "email@example.com" <firstname.lastname@example.org>, Linux Kernel Mailing List <email@example.com>, Mark Brown <firstname.lastname@example.org>, Sekhar Nori <email@example.com>, Chunyan Zhang <firstname.lastname@example.org> 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) In-Reply-To: <email@example.com> 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 >>> 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? > > 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 rather poor. 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 best sense. Maybe Adrian also have some thoughts? Kind regards Uffe
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
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=CAPDyKFpomN9KyX5u8C9-gBwBNm-sdfHwxbDVYD0hs73WFJR53A@mail.gmail.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --subject='Re: [PATCH RFC 2/3] mmc: sdhci-omap: Add using external dma' \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).