Subject: [PATCH] ARM: imx: i.mx6d/q: disable the double linefill feature of PL310

From: [email-masked] (Dirk Behme)
Date: Fri, 13 Sep 2013 18:46:06 +0200

Am 13.09.2013 09:48, schrieb Jason Liu:
> The L2 cache controller(PL310) version on the i.MX6D/Q is r3p1-50rel0
> The L2 cache controller(PL310) version on the i.MX6DL/SOLO/SL is r3p2
> But according to ARM PL310 errata: 752271
> ID: 752271: Double linefill feature can cause data corruption
> Fault Status: Present in: r3p0, r3p1, r3p1-50rel0. Fixed in r3p2
> Workaround: The only workaround to this erratum is to disable the
> double linefill feature. This is the default behavior.
>
> without this patch, you will meet the following error when run the
> memtester application at: http://pyropus.ca/software/memtester/
>
> FAILURE: 0x00100000 != 0x00200000 at offset 0x01365664.
> FAILURE: 0x00100000 != 0x00200000 at offset 0x01365668.
> FAILURE: 0x00100000 != 0x00200000 at offset 0x0136566c.
> FAILURE: 0x00100000 != 0x00200000 at offset 0x01365670.
> FAILURE: 0x00100000 != 0x00200000 at offset 0x01365674.
> FAILURE: 0x00100000 != 0x00200000 at offset 0x01365678.
> FAILURE: 0x00100000 != 0x00200000 at offset 0x0136567c.
>
> Signed-off-by: Jason Liu <[email-masked]>
> ---
>   arch/arm/mach-imx/system.c |   13 ++++++++++++-
>   1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/mach-imx/system.c b/arch/arm/mach-imx/system.c
> index 64ff37e..0c3fa48 100644
> --- a/arch/arm/mach-imx/system.c
> +++ b/arch/arm/mach-imx/system.c
> @@ -116,7 +116,18 @@ void __init imx_init_l2cache(void)
>
>   	/* Configure the L2 PREFETCH and POWER registers */
>   	val = readl_relaxed(l2x0_base + L2X0_PREFETCH_CTRL);
> -	val |= 0x70800000;
> +	val |= 0x30000000;
> +	/*
> +	 * The L2 cache controller(PL310) version on the i.MX6D/Q is r3p1-50rel0
> +	 * The L2 cache controller(PL310) version on the i.MX6DL/SOLO/SL is r3p2
> +	 * But according to ARM PL310 errata: 752271
> +	 * ID: 752271: Double linefill feature can cause data corruption
> +	 * Fault Status: Present in: r3p0, r3p1, r3p1-50rel0. Fixed in r3p2
> +	 * Workaround: The only workaround to this erratum is to disable the
> +	 * double linefill feature. This is the default behavior.
> +	 */
> +	if (!of_machine_is_compatible("fsl,imx6q"))
> +		val |= 0x40800000;

I've been thinking about this issue some time, too. Therefore two 
questions:

* Why do you set the 0x8 in 0x40800000 only in the non-imx6q case 
here? This bit shouldn't be affected by the errata and therefore could 
be set in all cases?

* To make it more clear what we do here (and in case somebody, e.g. a 
boot loader?) has already set bit 30, I would do something like:

val |= 0x70800000;
if (!of_machine_is_compatible("fsl,imx6q"))
	val &= ~(1 << 30);

What do you think?

Best regards

Dirk