From mboxrd@z Thu Jan 1 00:00:00 1970 From: neidhard.kim@lge.com (Jongsung Kim) Date: Mon, 12 Oct 2015 14:30:39 +0900 Subject: [PATCH] ARM:mm: fix kmap_atomic_to_page In-Reply-To: <20151007090121.GC21513@n2100.arm.linux.org.uk> References: <1444129773-12632-1-git-send-email-chanho.min@lge.com> <20151006192836.GX21513@n2100.arm.linux.org.uk> <5614979C.30100@lge.com> <20151007090121.GC21513@n2100.arm.linux.org.uk> Message-ID: <561B457F.5090104@lge.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org We tried to utilize a HW compressor as a zram backend. Current zram uses kmap_atomic to map a page, and the HW DMAes. So we needed to use kmap_atomic_to_page to get the page to be dma-mapped. On 10/07/2015 06:01 PM, Russell King - ARM Linux wrote: > On Wed, Oct 07, 2015 at 12:55:08PM +0900, Jongsung Kim wrote: >> Recently, we made a driver utilizing kmap_atomic_to_page. Of course, >> it's not mainlined. People may be using it outside mainline just like us. > Since kmap_atomic() mappings are supposed to be short-lived, why do you > need it in your driver? Don't you already have the struct page pointer > when setting up the kmap_atomic() mapping? > > It is invalid to setup a mapping, and leave it setup across any context > switching or similar. > > Also, kmap_atomic_to_page() is not exported to modules, so you can only > use it when built-in. > >> vmalloc has vmalloc_to_page, pkmap has kmap_to page, and fixmap has >> kmap_atomic_to_page. Then.. how about letting virt_to_page do them all? > No. virt_to_page() is defined to only work on the lowmem mapping, and > that's not going to change. > > Please show the outline of your code making use of this function so we > can better understand your use case. >