Hi Konrad,
On Thu, Oct 19, 2017 at 2:24 AM, Konrad Rzeszutek Wilk
<[email protected]> wrote:
> On Tue, Oct 17, 2017 at 10:02:50AM +0200, Geert Uytterhoeven wrote:
>> On Tue, Oct 17, 2017 at 9:30 AM, Yoshihiro Shimoda
>> <[email protected]> wrote:
>> > Since the commit de3ee99b097d ("mmc: Delete bounce buffer handling")
>> > deletes the bounce buffer handling, a request data size will be referred
>> > to max_{req,seg}_size instead of MMC_QUEUE_BOUNCESZ (64k bytes).
>> >
>> > In other hand, renesas_sdhi_internal_dmac.c will set very big value of
>> > max_{req,seg}_size because the max_blk_count is set to 0xffffffff.
>> > And then, "swiotlb buffer is full" happens because swiotlb can handle
>> > a memory size up to 256k bytes only (IO_TLB_SEGSIZE = 128 and
>> > IO_TLB_SHIFT = 11).
>> >
>> > So, this patch fixes the issue to set max_blk_count to 512. Then,
>> > the max_{req,seg}_size will be set to 256k bytes.
>> >
>> > Reported-by: Dirk Behme <[email protected]>
>> > Signed-off-by: Yoshihiro Shimoda <[email protected]>
>>
>> Thanks for your patch!
>>
>> > ---
>> > drivers/mmc/host/renesas_sdhi_internal_dmac.c | 5 +++--
>> > 1 file changed, 3 insertions(+), 2 deletions(-)
>> >
>> > 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.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]
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
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