linux-kernel - Re: [PATCH v3 1/5] firmware: qcom_scm: provide a read-modify-write function

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Message-ID: <eb23cc13-9738-8e82-6b13-76cc7ccbe280@linaro.org>
Date:   Mon, 20 Mar 2023 17:35:53 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Mukesh Ojha <quic_mojha@...cinc.com>, agross@...nel.org,
        andersson@...nel.org, konrad.dybcio@...aro.org,
        linus.walleij@...aro.org
Cc:     linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-gpio@...r.kernel.org
Subject: Re: [PATCH v3 1/5] firmware: qcom_scm: provide a read-modify-write
 function



On 17/03/2023 16:27, Mukesh Ojha wrote:
> It was released by Srinivas K. that there is a need of
> read-modify-write scm exported function so that it can
> be used by multiple clients.
> 
> Let's introduce qcom_scm_io_update_field() which masks
> out the bits and write the passed value to that
> bit-offset. Subsequent patch will use this function.
> 
> Suggested-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
> Signed-off-by: Mukesh Ojha <quic_mojha@...cinc.com>
> ---
>   drivers/firmware/qcom_scm.c            | 15 +++++++++++++++
>   include/linux/firmware/qcom/qcom_scm.h |  2 ++
>   2 files changed, 17 insertions(+)
> 
> diff --git a/drivers/firmware/qcom_scm.c b/drivers/firmware/qcom_scm.c
> index 3e020d1..aca2556 100644
> --- a/drivers/firmware/qcom_scm.c
> +++ b/drivers/firmware/qcom_scm.c
> @@ -407,6 +407,21 @@ int qcom_scm_set_remote_state(u32 state, u32 id)
>   }
>   EXPORT_SYMBOL(qcom_scm_set_remote_state);
>   
> +int qcom_scm_io_update_field(phys_addr_t addr, unsigned int mask, unsigned int val)
> +{
> +	unsigned int old, new;
> +	int ret;
> +
> +	ret = qcom_scm_io_readl(addr, &old);
> +	if (ret)
> +		return ret;
> +
> +	new = (old & ~mask) | val;

thanks for doing this,

With field semantics, val should be shifted within the function, so the 
caller only sets value for field rather than passing a shifted value.
so this should be:

new = (old & ~mask) | (val << ffs(mask) - 1);


--srini



> +
> +	return qcom_scm_io_writel(addr, new);
> +}
> +EXPORT_SYMBOL(qcom_scm_io_update_field);
> +
>   static int __qcom_scm_set_dload_mode(struct device *dev, bool enable)
>   {
>   	struct qcom_scm_desc desc = {
> diff --git a/include/linux/firmware/qcom/qcom_scm.h b/include/linux/firmware/qcom/qcom_scm.h
> index 1e449a5..203a781 100644
> --- a/include/linux/firmware/qcom/qcom_scm.h
> +++ b/include/linux/firmware/qcom/qcom_scm.h
> @@ -84,6 +84,8 @@ extern bool qcom_scm_pas_supported(u32 peripheral);
>   
>   extern int qcom_scm_io_readl(phys_addr_t addr, unsigned int *val);
>   extern int qcom_scm_io_writel(phys_addr_t addr, unsigned int val);
> +extern int qcom_scm_io_update_field(phys_addr_t addr, unsigned int mask,
> +				    unsigned int val);
>   
>   extern bool qcom_scm_restore_sec_cfg_available(void);
>   extern int qcom_scm_restore_sec_cfg(u32 device_id, u32 spare);