From: Christoph Hellwig <hch@xxxxxx> Subject: mmc: JZ4740: remove the flush_kernel_dcache_page call in jz4740_mmc_read_data Patch series "_kernel_dcache_page fixes and removal". While looking to convert the block layer away from kmap_atomic towards kmap_local_page and prefeably the helpers that abstract it away I noticed that a few block drivers directly or implicitly call flush_kernel_dcache_page before kunmapping a page that has been written to. flush_kernel_dcache_page is documented to to be used in such cases, but flush_dcache_page is actually required when the page could be in the page cache and mapped to userspace, which is pretty much always the case when kmapping an arbitrary page. Unfortunately the documentation doesn't exactly make that clear, which lead to this misused. And it turns out that only the copy_strings / copy_string_kernel in the exec code were actually correct users of flush_kernel_dcache_page, which is why I think we should just remove it and eat the very minor overhead in exec rather than confusing poor driver writers. This patch (of 6): MIPS now implements flush_kernel_dcache_page (as an alias to flush_dcache_page). Link: https://lkml.kernel.org/r/20210712060928.4161649-1-hch@xxxxxx Link: https://lkml.kernel.org/r/20210712060928.4161649-2-hch@xxxxxx Signed-off-by: Christoph Hellwig <hch@xxxxxx> Acked-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: "James E.J. Bottomley" <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> Cc: Russell King <linux@xxxxxxxxxxxxxxx> Cc: Guo Ren <guoren@xxxxxxxxxx> Cc: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx> Cc: Nick Hu <nickhu@xxxxxxxxxxxxx> Cc: Greentime Hu <green.hu@xxxxxxxxx> Cc: Vincent Chen <deanbo422@xxxxxxxxx> Cc: Helge Deller <deller@xxxxxx> Cc: Yoshinori Sato <ysato@xxxxxxxxxxxxx> Cc: Rich Felker <dalias@xxxxxxxx> Cc: Geoff Levand <geoff@xxxxxxxxxxxxx> Cc: Paul Cercueil <paul@xxxxxxxxxxxxxxx> Cc: Ulf Hansson <ulf.hansson@xxxxxxxxxx> Cc: Alex Shi <alexs@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- drivers/mmc/host/jz4740_mmc.c | 4 ---- 1 file changed, 4 deletions(-) --- a/drivers/mmc/host/jz4740_mmc.c~mmc-jz4740-remove-the-flush_kernel_dcache_page-call-in-jz4740_mmc_read_data +++ a/drivers/mmc/host/jz4740_mmc.c @@ -578,10 +578,6 @@ static bool jz4740_mmc_read_data(struct } } data->bytes_xfered += miter->length; - - /* This can go away once MIPS implements - * flush_kernel_dcache_page */ - flush_dcache_page(miter->page); } sg_miter_stop(miter); _
