linux-kernel - Re: [PATCH v4 12/12] interconnect: qcom: icc-rpm: Allow negative QoS offset

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Date:   Wed, 15 Feb 2023 03:16:40 +0200
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>,
        linux-arm-msm@...r.kernel.org, andersson@...nel.org,
        agross@...nel.org
Cc:     marijn.suijten@...ainline.org, Georgi Djakov <djakov@...nel.org>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 12/12] interconnect: qcom: icc-rpm: Allow negative QoS
 offset

On 14/02/2023 16:37, Konrad Dybcio wrote:
> In some very very very very unfortunate cases, the correct offset of
> the QoS registers will be.. negative. One such case is MSM8998, where
> The DDR BWMON occupies what-would-be-the-BIMC-base which we usually
> take into account with the register calculation, making the actual
> BIMC node start at what-would-be-the-BIMC-base+0x300.
> 
> In order to keep the calculation code sane, the simplest - however
> ugly it may be - solution is to allow the offset to be negative.

I'm not sure how does this work, as e.g. qcom_icc_set_qnoc_qos() will 
try to access an address before the first register. Most probably this 
patch should go together with the rest of msm8998 patches.

A slightly better solution to making qos_offset negative might be to 
make bwmon a child node of the icc.

> 
> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
> ---
>   drivers/interconnect/qcom/icc-rpm.h | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/interconnect/qcom/icc-rpm.h b/drivers/interconnect/qcom/icc-rpm.h
> index 77e263b93c27..5e4215f25c2e 100644
> --- a/drivers/interconnect/qcom/icc-rpm.h
> +++ b/drivers/interconnect/qcom/icc-rpm.h
> @@ -39,7 +39,7 @@ struct qcom_icc_provider {
>   	int num_intf_clks;
>   	enum qcom_icc_type type;
>   	struct regmap *regmap;
> -	unsigned int qos_offset;
> +	int qos_offset;
>   	u64 bus_clk_rate[2];
>   	bool keep_alive;
>   	struct clk_bulk_data bus_clks[2];
> @@ -105,7 +105,7 @@ struct qcom_icc_desc {
>   	bool keep_alive;
>   	enum qcom_icc_type type;
>   	const struct regmap_config *regmap_cfg;
> -	unsigned int qos_offset;
> +	int qos_offset;
>   };
>   
>   /* Valid for all bus types */

-- 
With best wishes
Dmitry