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authorLinus Walleij <linus.walleij@linaro.org>2016-11-25 12:35:00 +0300
committerUlf Hansson <ulf.hansson@linaro.org>2016-11-29 11:05:27 +0300
commit03d640ae1f9b24b1d2a11f747143a1ecc0745019 (patch)
treeed58f4741abe40f2bc5f7d9b2d7d0e3702de06d2 /include/linux/mmc
parentd3c6aac3bdfe97b8b44db6a8aba59786cb9531dc (diff)
downloadlinux-03d640ae1f9b24b1d2a11f747143a1ecc0745019.tar.xz
mmc: block: delete packed command support
I've had it with this code now. The packed command support is a complex hurdle in the MMC/SD block layer, around 500+ lines of code which was introduced in 2013 in commit ce39f9d17c14 ("mmc: support packed write command for eMMC4.5 devices") commit abd9ac144947 ("mmc: add packed command feature of eMMC4.5") ...and since then it has been rotting. The original author of the code has disappeared from the community and the mail address is bouncing. For the code to be exercised the host must flag that it supports packed commands, so in mmc_blk_prep_packed_list() which is called for every single request, the following construction appears: u8 max_packed_rw = 0; if ((rq_data_dir(cur) == WRITE) && mmc_host_packed_wr(card->host)) max_packed_rw = card->ext_csd.max_packed_writes; if (max_packed_rw == 0) goto no_packed; This has the following logical deductions: - Only WRITE commands can really be packed, so the solution is only half-done: we support packed WRITE but not packed READ. The packed command support has not been finalized by supporting reads in three years! - mmc_host_packed_wr() is just a static inline that checks host->caps2 & MMC_CAP2_PACKED_WR. The problem with this is that NO upstream host sets this capability flag! No driver in the kernel is using it, and we can't test it. Packed command may be supported in out-of-tree code, but I doubt it. I doubt that the code is even working anymore due to other refactorings in the MMC block layer, who would notice if patches affecting it broke packed commands? No one. - There is no Device Tree binding or code to mark a host as supporting packed read or write commands, just this flag in caps2, so for sure there are not any DT systems using it either. It has other problems as well: mmc_blk_prep_packed_list() is speculatively picking requests out of the request queue with blk_fetch_request() making the MMC/SD stack harder to convert to the multiqueue block layer. By this we get rid of an obstacle. The way I see it this is just cruft littering the MMC/SD stack. Cc: Namjae Jeon <namjae.jeon@samsung.com> Cc: Maya Erez <qca_merez@qca.qualcomm.com> Acked-by: Jaehoon Chung <jh80.chung@samsung.com> Signed-off-by: Linus Walleij <linus.walleij@linaro.org> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Diffstat (limited to 'include/linux/mmc')
-rw-r--r--include/linux/mmc/host.h5
1 files changed, 0 insertions, 5 deletions
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index 2a6418d0c343..2ce32fefb41c 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -494,11 +494,6 @@ static inline int mmc_host_uhs(struct mmc_host *host)
MMC_CAP_UHS_DDR50);
}
-static inline int mmc_host_packed_wr(struct mmc_host *host)
-{
- return host->caps2 & MMC_CAP2_PACKED_WR;
-}
-
static inline int mmc_card_hs(struct mmc_card *card)
{
return card->host->ios.timing == MMC_TIMING_SD_HS ||