Hi, On Tue, Jan 10, 2017 at 4:48 AM, Nikita Yushchenko <nikita.yoush@xxxxxxxxxxxxxxxxxx> wrote: > Hi > > There is a use cases when architecture is 64-bit but hardware supports > only DMA to lower 4G of address space. E.g. NVMe device on RCar PCIe host. > > For such cases, it looks proper to call blk_queue_bounce_limit() with > mask set to 0xffffffff - thus making block layer to use bounce buffers > for any addresses beyond 4G. To support that, architecture provides > GFP_DMA zone that covers exactly low 4G on arm64. > > However setting this limit does not work: > > if (b_pfn < (min_t(u64, 0xffffffffUL, BLK_BOUNCE_HIGH) >> PAGE_SHIFT)) > dma = 1; > > When mask is 0xffffffff that condition is false That should have been true in your case, since the b_pfn is smaller than 0xffffffff. > > q->limits.bounce_pfn = max(max_low_pfn, b_pfn); > > this line is executed and replaces any limit with end of memory (on > 64bit arch all memory is low). I don't understand why max() is used? And why not min()? Looks the above line just disables bounce for 64bit arch, doesn't it? Thanks, Ming > > > Not sure how to fix this properly. Any hints? > -- > To unsubscribe from this list: send the line "unsubscribe linux-block" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Ming Lei -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
