linux-kernel - Re: [PATCH] ARM: dts: at91: sama5d2: use the divided clock for SMC

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Date:   Tue, 20 Nov 2018 21:40:49 +0100
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Romain Izard <romain.izard.pro@...il.com>
Cc:     Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Tudor Ambarus <Tudor.Ambarus@...rochip.com>,
        Rob Herring <robh+dt@...nel.org>, mark.rutland@....com,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        devicetree@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: dts: at91: sama5d2: use the divided clock for SMC

On 20/11/2018 19:01:32+0100, Romain Izard wrote:
> Le mar. 20 nov. 2018 à 18:16, Alexandre Belloni
> <alexandre.belloni@...tlin.com> a écrit :
> >
> > Hello Romain,
> >
> > On 20/11/2018 17:57:37+0100, Romain Izard wrote:
> > > The SAMA5D2 is different from SAMA5D3 and SAMA5D4, as there are two
> > > different clocks for the peripherals in the SoC. The Static Memory
> > > controller is connected to the divided master clock.
> > >
> > > Unfortunately, the device tree does not correctly show this and uses the
> > > master clock directly. This clock is then used by the code for the NAND
> > > controller to calculate the timings for the controller, and we end up with
> > > slow NAND Flash access.
> > >
> > > Fix the device tree, and the performance of Flash access is improved.
> > >
> > > Signed-off-by: Romain Izard <romain.izard.pro@...il.com>
> > > ---
> > >  arch/arm/boot/dts/sama5d2.dtsi | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/arch/arm/boot/dts/sama5d2.dtsi b/arch/arm/boot/dts/sama5d2.dtsi
> > > index 61f68e5c48e9..b405992eb601 100644
> > > --- a/arch/arm/boot/dts/sama5d2.dtsi
> > > +++ b/arch/arm/boot/dts/sama5d2.dtsi
> > > @@ -308,7 +308,7 @@
> > >                                 0x1 0x0 0x60000000 0x10000000
> > >                                 0x2 0x0 0x70000000 0x10000000
> > >                                 0x3 0x0 0x80000000 0x10000000>;
> > > -                     clocks = <&mck>;
> > > +                     clocks = <&h32ck>;
> >
> > You will have to rebase on top of at91-dt. And if I'm not mistaken, this
> > line should be:
> >
> > +                       clocks = <&pmc PMC_TYPE_CORE PMC_MCK2>;
> >
> > >                       status = "disabled";
> > >
> > >                       nand_controller: nand-controller {
> 
> I guess you're right but this will only reach mainline in 4.21. I get slow
> flash access with 4.19 as well...
>

Ok, this is super annoying, I'll try to get that as fixes on v4.20 and
I'll rebase at91-dt on top of that...

-- 
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com