From mboxrd@z Thu Jan 1 00:00:00 1970 From: thomas@koeller.dyndns.org (Thomas Koeller) Date: Thu, 4 Mar 2010 22:11:08 +0100 Subject: DMA using data buffer vmapped in kernel space Message-ID: <201003042211.28569.thomas@koeller.dyndns.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi, I am writing a driver that loads a firmware blob into its device. The driver calls request_firmware() and gets a struct firmware * that contains a data buffer pointer in its 'data' member. The buffer is then passed to a SPI driver to send it to the device. The SPI driver uses DMA and, in preparation for that, eventually calls dma_cache_maint() (contained in arch/arm/mm/dma-mapping.c). At this point, the whole thing goes bad because there is a check: BUG_ON(!virt_addr_valid(start) || !virt_addr_valid(start + size - 1)); and the address obtained via request_firmware() fails this check. The request_firmware() function creates the data buffer by allocating a number of single pages in a loop, places them in an array, and finally creates a kernel mapping by calling vmap(). The vmap() result is the buffer address passed to the DMA. I do not understand the purpose of the failing check. The virt_addr_valid() macro checks whether its argument is below high_memory. But why would the virtual address of a DMA data buffer matter at all? After all, the pages are resident, so I cannot see any problem here. Can anybody explain? Thomas -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 490 bytes Desc: This is a digitally signed message part. URL: