linux-kernel - Re: [PATCH RFC] clk: mxs: Fix invalid 32-bit access to frac registers

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Message-ID: <1638147247.144508.1418577377536.JavaMail.open-xchange@oxbaltgw03.schlund.de>
Date:	Sun, 14 Dec 2014 18:16:17 +0100 (CET)
From:	Stefan Wahren <stefan.wahren@...e.com>
To:	Marek Vasut <marex@...x.de>
Cc:	linux-kernel@...r.kernel.org, festevam@...il.com,
	shawn.guo@...aro.org, mturquette@...aro.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH RFC] clk: mxs: Fix invalid 32-bit access to frac
 registers

Hi Marek,

> Marek Vasut <marex@...x.de> hat am 14. Dezember 2014 um 17:12 geschrieben:
>
> >
> > static void __iomem *digctrl;
> > #define DIGCTRL digctrl
> > @@ -118,11 +119,12 @@ static void __init clk_misc_init(void)
> > /*
> > * 480 MHz seems too high to be ssp clock source directly,
> > * so set frac0 to get a 288 MHz ref_io0 and ref_io1.
> > + * According to reference manual we must access frac0 bytewise.
> > */
> > - val = readl_relaxed(FRAC0);
> > - val &= ~((0x3f << BP_FRAC0_IO0FRAC) | (0x3f << BP_FRAC0_IO1FRAC));
> > - val |= (30 << BP_FRAC0_IO0FRAC) | (30 << BP_FRAC0_IO1FRAC);
> > - writel_relaxed(val, FRAC0);
> > + writeb_relaxed(0x3f, FRAC0 + FRAC0_IO0 + CLR);
> > + writeb_relaxed(30, FRAC0 + FRAC0_IO0 + SET);
> > + writeb_relaxed(0x3f, FRAC0 + FRAC0_IO1 + CLR);
> > + writeb_relaxed(30, FRAC0 + FRAC0_IO1 + SET);
>
> This used to be a R-M-W sequence, but now it's changed to multiple writes.
> This
> changes the behavior and seeing you use the CLR register, I am worried this
> might be prone to clock glitches. What do you think please ?

you are right. I adapt the imx23 init to the imx28 to make code simple. But it
would be better to avoid glitches.
I hope it's okay for this bugfix to introduce a R-M-W sequence for the imx23
init. So it's consequent.

>
> [...]
>
> Also, it might be a good idea to zap the 0x3f mask and use HEX and DEC numbers
> consistently, but this is an idea for another patch.

Yes.

Btw i hope this patch also fixes a SPI communication issue with our hardware
which forces us to bypass ref_io1 for ssp2.
But i will have access to that hardware tomorrow.

Thanks

Stefan

>
> Best regards,
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
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