On Mon, Nov 30, 2015 at 05:59:26PM -0800, Stefan Agner wrote:
> Linux on Vybrid used several different L2 latencies so far, none
> of them seem to be the right ones. According to the application note
> AN4947 ("Understanding Vybrid Architecture"), the tag portion runs
> on CPU clock and is inside the L2 cache controller, whereas the data
> portion is stored in the external SRAM running on platform clock.
> Hence it is likely that the correct value requires a higher data
> latency then tag latency.
>
> These are the values which have been used so far:
> - The mainline values:
> arm,data-latency = <1 1 1>;
> arm,tag-latency = <2 2 2>;
> Those values have lead to problems on higher clocks. They look
> like a poor translation from the reset values (missing +1 offset
> and a mix up between tag/latency values).
> - The Linux 3.0 (SoC vendor BSP) values (converted to DT notation):
> arm,data-latency = <4 2 3>
> arm,tag-latency = <4 2 3>
> The cache initialization function along with the value matches the
> i.MX6 code from the same kernel, so it seems that those values have
> just been copied.
> - The Colibri values:
> arm,data-latency = <2 1 2>;
> arm,tag-latency = <3 2 3>;
> Those were a mix between the values of the Linux 3.0 based BSP and
> the mainline values above.
> - The SoC Reset values (converted to DT notation):
> arm,data-latency = <3 3 3>;
> arm,tag-latency = <2 2 2>;
>
> So far there is no official statement on what the correct values are.
> See also the related Freescale community thread:
> https://community.freescale.com/message/579785#579785
>
> For now, the reset values seem to be the best bet. Remove all other
> "bogus" values and use the reset value on vf610.dtsi level.
>
> Signed-off-by: Stefan Agner <stefan@xxxxxxxx>
> ---
> Hi Shawn,
>
> Any chance to get this into 4.4?
I can try. Generally, upstream maintainers are becoming more strict for
-rc inclusion after -rc3 phase. Do you have any user stories about why
this is a critical/urgent fix? If we send this a critical fix for 4.4-rc
inclusion, do we need to Cc stable?
Shawn
>
> --
> Stefan
>
> arch/arm/boot/dts/vf610-colibri.dtsi | 5 -----
> arch/arm/boot/dts/vf610.dtsi | 2 +-
> 2 files changed, 1 insertion(+), 6 deletions(-)
>
> diff --git a/arch/arm/boot/dts/vf610-colibri.dtsi b/arch/arm/boot/dts/vf610-colibri.dtsi
> index 19fe045..2d7eab7 100644
> --- a/arch/arm/boot/dts/vf610-colibri.dtsi
> +++ b/arch/arm/boot/dts/vf610-colibri.dtsi
> @@ -18,8 +18,3 @@
> reg = <0x80000000 0x10000000>;
> };
> };
> -
> -&L2 {
> - arm,data-latency = <2 1 2>;
> - arm,tag-latency = <3 2 3>;
> -};
> diff --git a/arch/arm/boot/dts/vf610.dtsi b/arch/arm/boot/dts/vf610.dtsi
> index 5f8eb1b..58bc6e4 100644
> --- a/arch/arm/boot/dts/vf610.dtsi
> +++ b/arch/arm/boot/dts/vf610.dtsi
> @@ -19,7 +19,7 @@
> reg = <0x40006000 0x1000>;
> cache-unified;
> cache-level = <2>;
> - arm,data-latency = <1 1 1>;
> + arm,data-latency = <3 3 3>;
> arm,tag-latency = <2 2 2>;
> };
> };
> --
> 2.6.2
>
>
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