On 13/01/15 16:22, Ulf Hansson wrote: > On 13 January 2015 at 14:23, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote: >> On 13/01/15 13:25, Ulf Hansson wrote: >>> Hi Adrian, >>> >>> Thanks for working on this and apologize for my late reply! >>> >>> On 5 December 2014 at 18:41, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote: >>>> Currently, there is core support for tuning during >>>> initialization. There can also be a need to re-tune >>>> periodically (e.g. sdhci) or to re-tune after the >>>> host controller is powered off (e.g. after PM >>>> runtime suspend / resume) or to re-tune in response >>>> to CRC errors. >>>> >>>> The main requirements for re-tuning are: >>>> - ability to enable /disable re-tuning >>>> - ability to flag that re-tuning is needed >>>> - ability to re-tune before any request >>>> - ability to hold off re-tuning if the card is busy >>>> - ability to hold off re-tuning if re-tuning is in >>>> progress >>>> - ability to run a re-tuning timer >>> >>> I suggest we skip the support for the re-tuning timer in this initial >>> step and thus remove the related functionality from this patchset. It >>> adds complexity, but more important it's not obvious that it actually >>> will help. I am more concerned that it randomly will cause a request >>> latency and thus decrease performance. >>> >>> The re-tuning period can't be selected "perfectly", so in this initial >>> step let's instead just rely on re-tune from the request retry path. >>> >>> If we do see a need for a doing re-tuning periodically, how about >>> using the runtime PM suspend path (of the mmc card device). In that >>> way, we should be able to minimize the impact on performance. >> >> Thank you for looking at the patches. >> >> I am not sure I know what you mean. sdhci already has a re-tuning timer, so >> this is just moving it into core, where it won't be used by other drivers >> unless they enable it. > > I am kind of questioning the re-tuning timer in sdhci. What is it good for? It is part of the SD Host Controller Standard Specification. The timer ensures that re-tuning is done before temperature changes could affect the "sampling point". It is needed for re-tuning mode 1 for UHS-I modes like SDR104. > > Can sdhci rely on that the mmc core performs a re-tune from the > request retry mechanism instead? Not according to the standard. > >> >> I am not sure what you want to leave in sdhci.c and what you want in core, >> if anything. > > We need all the infrastructure code in the core. Much like what your > patchset does. Except that I would like you to remove the option of > having a timer and the corresponding complexity it adds. If we are going to follow the standard then that doesn't seem to be an option. > >> >> At a minimum I need sdhci to be able to switch from hs400 to hs200, re-tune, >> and switch back. > > As stated, I am only questioning the timer, nothing else. Ok so how should I proceed? -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
