From mboxrd@z Thu Jan 1 00:00:00 1970 From: inki.dae@samsung.com (daeinki) Date: Fri, 07 Jan 2011 19:02:14 +0900 Subject: Memory sharing issue by application on V4L2 based device driver with system mmu. In-Reply-To: <1294390465.6019.212.camel@thor.local> References: <4D25BC22.6080803@samsung.com> <002201cbadfd$6d59e490$480dadb0$%han@samsung.com> <1294390465.6019.212.camel@thor.local> Message-ID: <4D26E4A6.2020103@samsung.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Michel D?nzer ? ?: > On Fre, 2011-01-07 at 11:17 +0900, InKi Dae wrote: >> thank you for your comments. >> >> your second comment has no any problem as I said before, user virtual >> addess could be translated in page unit. but the problem, as you said, >> is that when cpu access to the memory in user mode, the memory >> allocated by malloc, page fault occurs so we can't find pfn to user >> virtual address. I missed that. but I think we could resolve this one. >> >> as before, user application allocates memory through malloc function >> and then send it to device driver(using userptr feature). if the pfn >> is null when device driver translated user virtual address in page >> unit then it allocates phsical memory in page unit using some >> interface such as alloc_page() and then mapping them. when pfn is >> null, to check it and allocate physical memory in page unit could be >> processed by videobuf2. >> >> of course, videobuf2 has no any duty considered for system mmu. so >> videobuf2 just provides callback for 3rd party and any platform with >> system mmu such as Samsung SoC C210 implements the function(allocating >> physical memory and mapping it) and registers it to callback of >> videobuf2. by doing so, I think your first comment could be cleared. > > FWIW, TTM (drivers/gpu/drm/ttm, include/drm/ttm) is designed and used > for managing memory between CPU/GPU and kernel/userspace access. I > haven't looked at your requirements in detail, but if you haven't looked > at TTM yet, it sounds like it might be worth a look. > > Thank you for your advice. I would look at TTM driver.