From mboxrd@z Thu Jan 1 00:00:00 1970 From: m.szyprowski@samsung.com (Marek Szyprowski) Date: Tue, 27 Jul 2010 15:46:26 +0200 Subject: [PATCHv2 2/4] mm: cma: Contiguous Memory Allocator added In-Reply-To: <20100727065842.40ae76c8@bike.lwn.net> References: <743102607e2c5fb20e3c0676fadbcb93d501a78e.1280151963.git.m.nazarewicz@samsung.com> <20100727120841.GC11468@n2100.arm.linux.org.uk> <003701cb2d89$adae4580$090ad080$%szyprowski@samsung.com> <20100727065842.40ae76c8@bike.lwn.net> Message-ID: <003f01cb2d92$20819730$6184c590$%szyprowski@samsung.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hello, On Tuesday, July 27, 2010 2:59 PM Jonathan Corbet wrote: > On Tue, 27 Jul 2010 14:45:58 +0200 > Marek Szyprowski wrote: > > > > How does one obtain the CPU address of this memory in order for the CPU > > > to access it? > > > > Right, we did not cover such case. In CMA approach we tried to separate > > memory allocation from the memory mapping into user/kernel space. Mapping > > a buffer is much more complicated process that cannot be handled in a > > generic way, so we decided to leave this for the device drivers. Usually > > video processing devices also don't need in-kernel mapping for such > > buffers at all. > > Still...that *is* why I suggested an interface which would return both > the DMA address and a kernel-space virtual address, just like the DMA > API does... Either that, or just return the void * kernel address and > let drivers do the DMA mapping themselves. Returning only the > dma_addr_t address will make the interface difficult to use in many > situations. As I said, drivers usually don't need in-kernel mapping for video buffers. Is there really a need for creating such mapping? Best regards -- Marek Szyprowski Samsung Poland R&D Center