linux-kernel - Re: [PATCH v2 03/13] arm64: dts: qcom: sdm845: Fix the base addresses of LLCC banks

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Date:   Tue, 13 Dec 2022 17:27:45 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        andersson@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, bp@...en8.de,
        tony.luck@...el.com
Cc:     quic_saipraka@...cinc.com, konrad.dybcio@...aro.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        james.morse@....com, mchehab@...nel.org, rric@...nel.org,
        linux-edac@...r.kernel.org, quic_ppareek@...cinc.com,
        luca.weiss@...rphone.com, stable@...r.kernel.org
Subject: Re: [PATCH v2 03/13] arm64: dts: qcom: sdm845: Fix the base addresses
 of LLCC banks

On 12/12/2022 13:33, Manivannan Sadhasivam wrote:
> The LLCC block has several banks each with a different base address
> and holes in between. So it is not a correct approach to cover these
> banks with a single offset/size. Instead, the individual bank's base
> address needs to be specified in devicetree with the exact size.
> 
> Also, let's get rid of reg-names property as it is not needed anymore.
> The driver is expected to parse the reg field based on index to get the
> addresses of each LLCC banks.
> 
> Cc: <stable@...r.kernel.org> # 5.4

No, you cannot backport it. You will break users.

> Fixes: ba0411ddd133 ("arm64: dts: sdm845: Add device node for Last level cache controller")
> Reported-by: Parikshit Pareek <quic_ppareek@...cinc.com>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> ---
>  arch/arm64/boot/dts/qcom/sdm845.dtsi | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/boot/dts/qcom/sdm845.dtsi b/arch/arm64/boot/dts/qcom/sdm845.dtsi
> index 65032b94b46d..683b861e060d 100644
> --- a/arch/arm64/boot/dts/qcom/sdm845.dtsi
> +++ b/arch/arm64/boot/dts/qcom/sdm845.dtsi
> @@ -2132,8 +2132,9 @@ uart15: serial@...000 {
>  
>  		llcc: system-cache-controller@...0000 {
>  			compatible = "qcom,sdm845-llcc";
> -			reg = <0 0x01100000 0 0x31000>, <0 0x01300000 0 0x50000>;
> -			reg-names = "llcc_base", "llcc_broadcast_base";

Once property was made required, you cannot remove it. What if other
bindings user depends on it?

Please instead keep/update the reg-names and/or mark it as deprecated.
It must stay in DTS for some time.

Best regards,
Krzysztof