Hi, Uffe >>>On 19 March 2017 at 01:45, Bean Huo (beanhuo) <beanhuo@xxxxxxxxxx> >wrote: >>>> This patch fixes the issue that mmc_blk_issue_rq still flushes cache >>>> when eMMC cache has already been off through user space tool, such >>>> as mmc-utils. >>>> The reason is that card->ext_csd.cache_ctrl isn't reset. >>> >>>First, why do you want to turn of the cache ctrl? Is the eMMC device >>>having issues with it? Then we should invent a card quirk instead. >> >> >> Why I turn off it? because I did power loss testing and validation, I should >switch it off and on. >> When I do some performance and power loss case validation on several >> Linux release versions, I need to switch off or on cache through user space tool. >> I can't confirm every user that likes me, But I think at least it is >> not reasonable to flush eMMC cache, when internal eMMC cache is off. > >Ah, I see. Your use-case seems reasonable while validating robustness of the >eMMC! > >> >>>Second, what errors do you encounter when the mmc core tries to flush >>>the cache when it has been turned off? Can you please elaborate on this? >> >> >> No error found, but firstly, please think about overhead introduced by >> useless flush cache, Unless you Don't care this tiny time. second, >> under the condition of cache off, additional flush cache request still has impact >>on Internal eMMC logic. I don't know What and how impact, but at least it is >>really exist. > >Got it! > >However I still don't like the mmc ioctls API to compensate and deal with all >"crazy-ness" that user-space may cause. Cache-ctrl is only one case out of many. Question is that not every Linux-mmc user really understand that shouldn't use "mmc ioctls API to compensate and deal with all crazy-ness that user-space may cause ". no matter we like or dislike, Issue is already there; I think that most of eMMC user is now configuring eMMC through mmc-utils and mmc ioctls. This is a real condition. Some automotive applications, Cache would not be enabled. Maybe I am shallow, mmc ioctls likes backdoor that let user access and configure eMMC some feature, Even not too often. I still suggest to fix this in mmc ioctls, unless mmc iotcls being deleted, and mmc-utils doesn't support Cache off/on. Because eMMC internal cache has been disabled, but Linux-mmc still issue flush cache request, this is indeed Not reasonable. It definitely increases system level overhead. >I see two viable options to solve your problem. >1) Extend mmc_test with a new test(s) for cache ctrl and perhaps suspend/resume. >Isn't this actually exactly what you want? >2) Extend debugfs to be able to turn cache ctrl on/off. I can try, but this patch is just to fix mmc ctrls backdoor on eMMC flush cache. >[...] > >Kind regards >Uffe >-- >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 ��.n��������+%������w��{.n�����{��i��)�� jg��� �����ݢj����G���� ���j:+v���w�m������w�������h�����٥
