On Fri, Oct 20, 2017 at 03:18:55AM +0000, Yoshihiro Shimoda wrote: > Hi again! > > > From: Yoshihiro Shimoda, Sent: Thursday, October 19, 2017 8:39 PM > > > > Hi Geert-san, Konrad-san, > > > > > From: Geert Uytterhoeven, Sent: Thursday, October 19, 2017 5:34 PM > > > > > > Hi Konrad, > > > > > > On Thu, Oct 19, 2017 at 2:24 AM, Konrad Rzeszutek Wilk > > > <konrad@xxxxxxxxxx> wrote: > < snip > > > > >> > diff --git a/drivers/mmc/host/renesas_sdhi_internal_dmac.c b/drivers/mmc/host/renesas_sdhi_internal_dmac.c > > > >> > index f905f23..6c9b4b2 100644 > > > >> > --- a/drivers/mmc/host/renesas_sdhi_internal_dmac.c > > > >> > +++ b/drivers/mmc/host/renesas_sdhi_internal_dmac.c > > > >> > @@ -80,8 +80,9 @@ > > > >> > .scc_offset = 0x1000, > > > >> > .taps = rcar_gen3_scc_taps, > > > >> > .taps_num = ARRAY_SIZE(rcar_gen3_scc_taps), > > > >> > - /* Gen3 SDHI DMAC can handle 0xffffffff blk count, but seg = 1 */ > > > >> > - .max_blk_count = 0xffffffff, > > > >> > + /* The swiotlb can handle memory size up to 256 kbytes for now. */ > > > >> > + .max_blk_count = 512, > > > >> > > > >> Fixing this in the individual drivers feels like the wrong solution to me. > > > >> > > > >> 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 > > > > So, how do we handle to resolve (or avoid) the issue? > > 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? > https://patchwork.kernel.org/patch/10018879/ Why not use IO_TLB_SEGSIZE << IO_TLB_SHIFT or alternatively swiotlb_max_segment? See 5584f1b1d73e9
