linux-kernel - Re: [PATCH V7 1/2] csky/dma: bugfix dma_sync_for

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Message-ID: <20180925113824.GA7183@guoren>
Date:   Tue, 25 Sep 2018 19:38:24 +0800
From:   Guo Ren <ren_guo@...ky.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <marc.zyngier@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh@...nel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        c-sky_gcc_upstream@...ky.com, gnu-csky@...tor.com,
        Greentime Hu <green.hu@...il.com>
Subject: Re: [PATCH V7 1/2] csky/dma: bugfix dma_sync_for_cpu/device

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@...ky.com> 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@...ky.com> 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@...ky.com>
> > >
> > > 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@n2100.armlinux.org.uk/
> > 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