linux-kernel - Re: [PATCH v2 3/3] sh: dma: Correct the number of DMA channels in SH7709

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Date:   Tue, 4 Jul 2023 09:54:41 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
Cc:     Artur Rojek <contact@...ur-rojek.eu>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        Rafael Ignacio Zurita <rafaelignacio.zurita@...il.com>,
        linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] sh: dma: Correct the number of DMA channels in SH7709

Hi Adrian.

On Tue, Jul 4, 2023 at 9:43 AM John Paul Adrian Glaubitz
<glaubitz@...sik.fu-berlin.de> wrote:
> On Tue, 2023-07-04 at 09:32 +0200, Geert Uytterhoeven wrote:
> > On Tue, Jul 4, 2023 at 7:45 AM John Paul Adrian Glaubitz
> > <glaubitz@...sik.fu-berlin.de> wrote:
> > > On Sat, 2023-06-17 at 13:09 +0200, Geert Uytterhoeven wrote:
> > > > On Sat, Jun 17, 2023 at 9:32 AM John Paul Adrian Glaubitz
> > > > <glaubitz@...sik.fu-berlin.de> wrote:
> > > > > On Thu, 2023-06-08 at 12:03 +0200, John Paul Adrian Glaubitz wrote:
> > > > > > > > > That is actually safer, as the user can override NR_ONCHIP_DMA_CHANNELS
> > > > > > > > > when configuring his kernel, thus breaking DMA  due to an incorrect
> > > > > > > > > value of SH_DMAC_NR_MD_CH.
> > > > > > > > >
> > > > > > > > > Unfortunately we cannot protect against that when using a single DMAC,
> > > > > > > > > as SH_DMAC_NR_MD_CH can be either 4, 6, or 8.
> > > > > > > > >
> > > > > > > > > Perhaps this configuration should be moved from Kconfig to <cpu/dma.h>,
> > > > > > > > > to protect against a user overriding this value?
> > > > > > > >
> > > > > > > > Isn't SH_DMAC_NR_MD_CH already hardwired to the SoC being used?
> > > > > > >
> > > > > > > It depends on CONFIG_NR_ONCHIP_DMA_CHANNELS, while it
> > > > > > > should be fixed based on the SoC.
> > > > > >
> > > > > > I agree. However, I would be fine with merging this patch set first and fixing
> > > > > > this particular issue in a follow-up series.
> > > > >
> > > > > So, my suggestion is to take this series as-is for 6.5, then get the other issues
> > > > > you mentioned fixed for 6.6. I think it's already a gain when these issues are
> > > > > fixed and the kernel boots on the HP Journada 680 again.
> > > >
> > > > Sure, I don't want to block the acceptance of this series at all.
> > > > Thanks!
> > >
> > > Apologies for the late reply. Would you mind adding your Reviewed-by to this patch
> > > before I review and apply the series?
> >
> > With "must be a multiply of two" and "Must be an even number" removed.
> > Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
>
> Thanks. I guess, I will drop the whole
>
>         "and clarify that NR_ONCHIP_DMA_CHANNELS must be a multiply of two"
>
> then. Correct?

Correct. Also in the help text.
Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

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