On Mon, May 22, 2017 at 9:42 AM, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote: > On 19 May 2017 at 15:37, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote: >> The debugfs file "status" (in e.g. /debug/mmc3/mmc3:0001) is >> only available if and only if the card used is an (e)MMC or >> SD card, not for SDIO, as can be seen from this guard in >> mmc_add_card_debugfs(); >> >> if (mmc_card_mmc(card) || mmc_card_sd(card)) >> (...create debugfs "status" entry...) >> >> Further this debugfs entry suffers from all the same starvation >> issues as the other userspace things, under e.g. a heavy >> dd operation. >> >> It is therefore logical to move this over to the block layer >> when it is enabled, using the new custom requests and issue >> it using the block request queue. >> >> This makes this debugfs card access land under the request >> queue host lock instead of orthogonally taking the lock. >> >> Tested during heavy dd load by cat:in the status file. We >> add IS_ENABLED() guards and keep the code snippet just >> issueing the card status as a static inline in the header >> so we can still have card status working when the block >> layer is compiled out. > > Seems like a bit of re-factoring/cleanup could help here as > preparation step. I just posted a patch [1] cleaning up how the mmc > block layer fetches the card's status. > > Perhaps that could at least simplify a bit for $subject patch, > especially since it also makes mmc_send_status() being exported. OK if you merge your stuff I can iterate my patches on top, no problem. >> +#if IS_ENABLED(CONFIG_MMC_BLOCK) > > What wrong with a regular ifdefs stubs? Why do you need IS_ENABLED()? This is because the entire block layer can be compiled as a module. In that case CONFIG_MMC_BLOCK contains 'm' instead of 'y' which confusingly does not evaluate to true in the preprocessor (it assumes it is a misspelled 'n' I guess). And then the autobuilders wreak havoc. And that is why the IS_ENABLED() defines exist in the first place IIUC. I'm all for making CONFIG_MMC_BLOCK into a bool... but don't know how people (Intel laptops) feel about that extra code in their kernel at all times. >> void mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req); > > I don't get what mmc_blk_issue_rq() has to do with this change? Could > you please explain? If we start doing stubs we should stub everything IMO, but if you prefer I can make that a separate patch. Seems a bit overdone though. > Hmm, this thing seems a bit upside-down. > > Currently it's possible to build the mmc block device driver as a > module. In cases like this, accessing the card debugs node to request > the card's status, would trigger a call to mmc_blk_card_status_get(). > How would that work when the mmc block device driver isn't loaded and > probed? Module symbol resolution and driver loading is always necessary, it is no different for e.g. a wifi driver using the 802.11 library. It is definately possible to shoot oneself in the foot, but I think udev & friends usually load things in the right order? > It seems like the life cycle of the card debugfs node is now being > controlled as when the mmc block device driver has been successfully > probed. We need to deal with that somehow. Only for these two files but yes. ext_csd is a bit dubious as it is only available on storage devices (eMMC) that can not be SD, SDIO or combo cards, and we could make it only appear if using the block layer. The card status however we need to keep if people want it. We *COULD* consider just thrashing these debugfs files. It is not technically ABI and I wonder who is actually using them. Yours, Linus Walleij
