On Wed, Apr 11, 2018 at 10:08:06AM +0200, Boris Brezillon wrote: > On Wed, 11 Apr 2018 09:36:56 +0200 > Ladislav Michl <ladis@xxxxxxxxxxxxxx> wrote: > > > Hi Boris, > > > > On Wed, Apr 11, 2018 at 09:15:28AM +0200, Boris Brezillon wrote: [...] > > > Not sure this approach is safe on all archs: if the cache is VIVT or > > > VIPT, you may have several entries pointing to the same phys page, and > > > then, when dma_map_page() does its cache maintenance operations, it's > > > only taking one of these entries into account. > > > > Hmm, I used the same approach Samsung OneNAND driver does since commit > > dcf08227e964a53a2cb39130b74842c7dcb6adde. > > Both TI OMAP3630 and Samsung S5PC110 are using Cortex-A8 which > > is VIPT. In that case samsung's driver code has the same problem. > > > > > In other parts of the MTD subsystem, we tend to not do DMA on buffers > > > that have been vmalloc-ed. > > > > > > You can do something like > > > > > > if (virt_addr_valid(buf)) > > > /* Use DMA */ > > > else > > > /* > > > * Do not use DMA, or use a bounce buffer > > > * allocated with kmalloc > > > */ > > > > Okay, I'll use this approach then, but first I'd like to be sure above is > > correct. Anyone? > > See this discussion [1]. The problem came up a few times already, so > might find other threads describing why it's not safe. > > [1]https://lists.linuxfoundation.org/pipermail/iommu/2016-March/016240.html Question was more likely whenever there might exist more that one mapping of the same page. But okay, I'll disable DMA for highmem. Patch will follow. ladis -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
