Hi Laura, When we enable kernel v4.4 or newer version on our platform, we meet the issue of flushing cache without reference device. It seems that this patch set is a solution. I'm curious the progress of the discussion. Do you have any plan to fix it in v4.4 and newer kernel verison? On 2016/9/14 2:41, Laura Abbott wrote: > On 09/13/2016 08:14 AM, Will Deacon wrote: >> On Tue, Sep 13, 2016 at 08:02:20AM -0700, Laura Abbott wrote: >>> On 09/13/2016 02:19 AM, Will Deacon wrote: >>>> On Mon, Sep 12, 2016 at 02:32:56PM -0700, Laura Abbott wrote: >>>>> >>>>> arm64 may need to guarantee the caches are synced. Implement versions of >>>>> the kernel_force_cache API to allow this. >>>>> >>>>> Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx> >>>>> --- >>>>> v3: Switch to calling cache operations directly instead of relying on >>>>> DMA mapping. >>>>> --- >>>>> arch/arm64/include/asm/cacheflush.h | 8 ++++++++ >>>>> arch/arm64/mm/cache.S | 24 ++++++++++++++++++++---- >>>>> arch/arm64/mm/flush.c | 11 +++++++++++ >>>>> 3 files changed, 39 insertions(+), 4 deletions(-) >>>> >>>> I'm really hesitant to expose these cache routines as an API solely to >>>> support a driver sitting in staging/. I appreciate that there's a chicken >>>> and egg problem here, but we *really* don't want people using these routines >>>> in preference to the DMA API, and I fear that we'll simply grow a bunch >>>> more users of these things if we promote it as an API like you're proposing. >>>> >>>> Can the code not be contained under staging/, as part of ion? >>>> >>> >>> I proposed that in V1 and it was suggested I make it a proper API >>> >>> http://www.mail-archive.com/driverdev-devel@xxxxxxxxxxxxxxxxxxxxxx/msg47654.html >>> http://www.mail-archive.com/driverdev-devel@xxxxxxxxxxxxxxxxxxxxxx/msg47672.html >> >> :/ then I guess we're in disagreement. If ion really needs this stuff >> (which I don't fully grok), perhaps we should be exposing something at >> a higher level from the architecture, so it really can't be used for >> anything other than ion. > > I talked/complained about this at a past plumbers. The gist is that Ion > ends up acting as a fake DMA layer for clients. It doesn't match nicely > because clients can allocate both coherent and non-coherent memory. > Trying to use dma_map doesn't work because a) a device for coherency isn't > known at allocation time b) it kills performance. Part of the motivation > for taking this approach is to avoid the need to rework the existing > Android userspace and keep the existing behavior, as terrible as it > is. Having Ion out of staging and not actually usable isn't helpful. > > I'll give this all some more thought and hopefully have one or two more > proposals before Connect/Plumbers. > >> >> Will >> > > Thanks, > Laura > _______________________________________________ > Linaro-mm-sig mailing list > Linaro-mm-sig@xxxxxxxxxxxxxxxx > https://lists.linaro.org/mailman/listinfo/linaro-mm-sig _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
