Hi Konrad, On Fri, Nov 3, 2017 at 2:23 PM, Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx> wrote: > ..snip.. >> > > >> > > Anyway, I made v2 patches by using swiotlb related definitions. Would you check it? >> > >> > Did I miss that email? As in was I cc-ed? >> >> This was my fault. When I submitted v2 patches, I didn't include your email and iommu mailing list... > > No problem. >> >> > > https://patchwork.kernel.org/patch/10018879/ >> > >> > Why not use IO_TLB_SEGSIZE << IO_TLB_SHIFT or alternatively >> > swiotlb_max_segment? See 5584f1b1d73e9 >> >> I already made such a patch as v2 and it was merged into mmc.git / fixes branch. >> >> https://git.kernel.org/pub/scm/linux/kernel/git/ulfh/mmc.git/commit/?h=fixes&id=e90e8da72ad694a16a4ffa6e5adae3610208f73b > > What happens if the user has swiotlb=4096 on the command line (meaning > less than the default value)? Your max value will be incorrect. Could you use > swiotlb_max_segment? No, as that's the total size of the swiotlb buffer, not the maximum size of a single segment. Quoting an earlier part of the thread: On Thu, Oct 19, 2017 at 1:39 PM, Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx> wrote: >> >> iommu: Is there a better (generic) way to handle this? >> > >> > Yes. See 7453c549f5f6485c0d79cad7844870dcc7d1b34d, aka swiotlb_max_segment >> >> Thanks for the pointer! >> >> While I agree this can be used to avoid the swiotlb buffer full issue, >> I believe it is a suboptimal solution if the device actually uses an IOMMU. >> It limits the mapping size if CONFIG_SWIOTLB=y, which is always the >> case for arm/arm64 these days. > > I'm afraid but I misunderstood this API's spec when I read it at first. > After I tried to use it, I found the API cannot be used for a workaround because > this API returns total size of swiotlb. > > For example: > - The swiotlb_max_segment() returns 64M bytes from the API when a default setting. > - In this case, the maximum size per a map is 256k bytes. > - The swiotlb_max_segment() returns 128M bytes from the API when I added swiotlb=65536 > into the kernel parameter on arm64. > - In this case, the maximum size per a map is still 256k bytes because > the swiotlb has hardcoded the size by the following code: > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/lib/swiotlb.c?h=v4.14-rc5#n254 Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
