linux-kernel - Re: [PATCH 2/2] arm64: tegra: Mark BPMP channels as no-memory-wc

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Date:   Wed, 22 Jun 2022 16:29:03 +0300
From:   Mikko Perttunen <cyndis@...si.fi>
To:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Mikko Perttunen <mperttunen@...dia.com>,
        Mian Yousaf Kaukab <ykaukab@...e.de>,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] arm64: tegra: Mark BPMP channels as no-memory-wc

On 22.6.2022 16.23, Mikko Perttunen wrote:
> From: Mikko Perttunen <mperttunen@...dia.com>
> 
> The Tegra SYSRAM contains regions access to which is restricted to
> certain hardware blocks on the system, and speculative accesses to
> those will cause issues.
> 
> Patch 'misc: sram: Only map reserved areas in Tegra SYSRAM' attempted
> to resolve this by only mapping the regions specified in the device
> tree on the assumption that there are no such restricted areas within
> the 64K-aligned area of memory that contains the memory we wish to map.
> 
> Turns out this assumption is wrong, as there are such areas above the
> 4K pages described in the device trees. As such, we need to use the
> bigger hammer that is no-memory-wc, which causes the memory to be
> mapped as Device memory to which speculative accesses are disallowed.
> 
> As such, the previous patch in the series,
>    'firmware: tegra: bpmp: do only aligned access to IPC memory area',
> is required with this patch to make the BPMP driver only issue aligned
> memory accesses as those are also required with Device memory.
> 
> Fixes: fec29bf04994 ("misc: sram: Only map reserved areas in Tegra SYSRAM")
> Signed-off-by: Mikko Perttunen <mperttunen@...dia.com>
> ---

FWIW, with this, the aforementioned patch to misc/sram is redundant. It 
doesn't hurt, but doesn't really help either. Whether or not it should 
be reverted, I have no opinion.

Thanks,
Mikko

>   arch/arm64/boot/dts/nvidia/tegra186.dtsi | 1 +
>   arch/arm64/boot/dts/nvidia/tegra194.dtsi | 1 +
>   arch/arm64/boot/dts/nvidia/tegra234.dtsi | 1 +
>   3 files changed, 3 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/nvidia/tegra186.dtsi b/arch/arm64/boot/dts/nvidia/tegra186.dtsi
> index 0e9afc3e2f26..9eca18b54698 100644
> --- a/arch/arm64/boot/dts/nvidia/tegra186.dtsi
> +++ b/arch/arm64/boot/dts/nvidia/tegra186.dtsi
> @@ -1820,6 +1820,7 @@ sram@...00000 {
>   		#address-cells = <1>;
>   		#size-cells = <1>;
>   		ranges = <0x0 0x0 0x30000000 0x50000>;
> +		no-memory-wc;
>   
>   		cpu_bpmp_tx: sram@...00 {
>   			reg = <0x4e000 0x1000>;
> diff --git a/arch/arm64/boot/dts/nvidia/tegra194.dtsi b/arch/arm64/boot/dts/nvidia/tegra194.dtsi
> index d1f8248c00f4..3fdb0b852718 100644
> --- a/arch/arm64/boot/dts/nvidia/tegra194.dtsi
> +++ b/arch/arm64/boot/dts/nvidia/tegra194.dtsi
> @@ -2684,6 +2684,7 @@ sram@...00000 {
>   		#address-cells = <1>;
>   		#size-cells = <1>;
>   		ranges = <0x0 0x0 0x40000000 0x50000>;
> +		no-memory-wc;
>   
>   		cpu_bpmp_tx: sram@...00 {
>   			reg = <0x4e000 0x1000>;
> diff --git a/arch/arm64/boot/dts/nvidia/tegra234.dtsi b/arch/arm64/boot/dts/nvidia/tegra234.dtsi
> index cb3af539e477..0213a7e3dad0 100644
> --- a/arch/arm64/boot/dts/nvidia/tegra234.dtsi
> +++ b/arch/arm64/boot/dts/nvidia/tegra234.dtsi
> @@ -1325,6 +1325,7 @@ sram@...00000 {
>   		#address-cells = <1>;
>   		#size-cells = <1>;
>   		ranges = <0x0 0x0 0x40000000 0x80000>;
> +		no-memory-wc;
>   
>   		cpu_bpmp_tx: sram@...00 {
>   			reg = <0x70000 0x1000>;