Hello, Tom. On Wed, Aug 10, 2016 at 06:04:10PM +0800, Tom Yan wrote: > On 10 August 2016 at 11:26, Tejun Heo <tj@xxxxxxxxxx> wrote: > > Hmmm.. why not? The hardware limit is 64k and the driver is using a > > Is that referring to the maximum number of entries allowed in the > PRDT, Physical Region Descriptor Table (which is, more precisely, > 65535)? Yeap. > > Not necessarily. A single sg entry can point to an area larger than > > PAGE_SIZE. > > You mean the 4MB limit of "Data Byte Count" in "DW3: Description > Information" of the PRDT? Is that what max_segment_size (which is set > to a general fallback of 65536: > http://lxr.free-electrons.com/ident?i=dma_get_max_seg_size) is about > in this case? Ah, ahci isn't setting the hardware limit properly but yeah that's the maximum segment size. > And my point was, it will be a multiple of 168 anyway, if 1344 is just > an example. > > > As written above, that probably makes the ahci command table size > > nicely aligned. > > I think that's what bothers me ultimately, cause I don't see how 168 > makes it (more) nicely aligned (or even, aligned to what?). Hmmm... Looked at the sizes and they don't seem to align to anything meaningful. No idea. Thanks. -- tejun -- 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
