linux-kernel - Re: [PATCH 4/4] ARM: dts: Fix-up EMMC2 controller's frequency

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Message-ID: <78dec30c052e9bb76e52c38f3da5af371e5d65f5.camel@suse.de>
Date:   Wed, 24 Mar 2021 16:34:09 +0100
From:   Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To:     Stefan Wahren <stefan.wahren@...e.com>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-mmc@...r.kernel.org,
        devicetree@...r.kernel.org, bcm-kernel-feedback-list@...adcom.com,
        linux-rpi-kernel@...ts.infradead.org,
        Rob Herring <robh+dt@...nel.org>
Cc:     f.fainelli@...il.com, phil@...pberrypi.com,
        tim.gover@...pberrypi.com, adrian.hunter@...el.com,
        sbranden@...adcom.com, alcooperx@...il.com,
        linux-kernel@...r.kernel.org, ulf.hansson@...aro.org
Subject: Re: [PATCH 4/4] ARM: dts: Fix-up EMMC2 controller's frequency

Hi Stefan,

On Wed, 2021-03-24 at 16:16 +0100, Stefan Wahren wrote:
> Hi Nicolas,
> 
> Am 22.03.21 um 19:58 schrieb Nicolas Saenz Julienne:
> > From: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
> > 
> > Force emmc2's frequency to 150MHz as the default 100MHz (set by FW)
> > seems to interfere with the VPU clock when setup at frequencies bigger
> > than 500MHz (a pretty common case). This ends up causing unwarranted
> > SDHCI CMD hangs  when no SD card is present.
> > 
> > Signed-off-by: Nicolas Saenz Julienne <nsaenz@...nel.org>
> > ---
> >  arch/arm/boot/dts/bcm2711-rpi-4-b.dts | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/arch/arm/boot/dts/bcm2711-rpi-4-b.dts b/arch/arm/boot/dts/bcm2711-rpi-4-b.dts
> > index 3b4ab947492a..9aa8408d9960 100644
> > --- a/arch/arm/boot/dts/bcm2711-rpi-4-b.dts
> > +++ b/arch/arm/boot/dts/bcm2711-rpi-4-b.dts
> > @@ -257,6 +257,12 @@ &emmc2 {
> >  	vqmmc-supply = <&sd_io_1v8_reg>;
> >  	vmmc-supply = <&sd_vcc_reg>;
> >  	broken-cd;
> > +	/*
> > +	 * Force the frequency to 150MHz as the default 100MHz seems to
> > +	 * interfere with the VPU clock when setup at frequencies bigger than
> > +	 * 500MHz, causing unwarranted CMD hangs.
> > +	 */
> > +	clock-frequency = <150000000>;
> 
> i don't want to bike-shed here, but is there any chance to solve this in
> clk-bcm2835 in a less hacky way?

What do you have in mind?

All I can think of is adding some kind of heuristic to the clock's prepare()
callback. That said, I don't feel it would be a better solution than this.

Regards,
Nicolas



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