On Tue, Sep 25, 2018 at 11:59:48AM +0200, Arnd Bergmann wrote: > On Tue, Sep 25, 2018 at 11:46 AM Guo Ren <ren_guo@xxxxxxxxx> wrote: > > > > On Mon, Sep 24, 2018 at 10:38:04PM +0200, Arnd Bergmann wrote: > > > On Tue, Sep 18, 2018 at 3:48 PM Guo Ren <ren_guo@xxxxxxxxx> wrote: > > > > > > > > ref: https://lkml.org/lkml/2018/5/18/1068 > > > > > > > > map for_cpu for_device unmap > > > > TO_DEV writeback none writeback none > > > > TO_CPU invalidate invalidate* invalidate invalidate* > > > > BIDIR writeback invalidate writeback invalidate > > > > > > > > Signed-off-by: Guo Ren <ren_guo@xxxxxxxxx> > > > > > > Same comment as for the other patch: Explain why the original > > > version is wrong first. When giving a reference to some other > > > discussion, use the "Link" tag above your Signed-off-by line. > > > To point to a discussion on lkml, lore.kernel.org is the > > > recommended archive, so it would become > > > > > > Link: https://lore.kernel.org/lkml/20180518215548.GH17671@xxxxxxxxxxxxxxxxxxxxx/ > > Ok, I'll improve the comment: > > > > Fixup dma_mapping error in linux-4.19-rc3, and we must implement all > > DMA_TO_DEVICE/FROM_DEVICE/BIDIRECTIONAL for both sync_dma_for_device/cpu. > > The implementation of arch should follow the following rules: > > > > ... > > That seems ok, but it's better to start with a description of the problem > rather than the 'Fixup dma_mapping error in linux-4.19-rc3' part. > I would write this like: > > | The arch_sync_dma_for_cpu()/arch_sync_dma_for_device() > | implementation is broken for some combinations that end up > | in a BUG() instead of performing the necessary flushes. > | > | The implementation of arch should follow the following rules: > | ... > > The imperative 'Fix up dma_mapping error ...' is what belongs > into the subject line, and is ideally revisited at the end of the > changelog comment if you want to add more detail about what > you do. Nice tips, Thx. I'll continue to improve my comments. Best Regards Guo Ren
