Re: [PATCH v4 17/21] firmware: qcom_scm: provide a read-modify-write function

[Pavan Kondeti <quic_pkondeti@xxxxxxxxxxx>]

On Wed, Jun 28, 2023 at 06:04:44PM +0530, Mukesh Ojha wrote:
> It was realized 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@xxxxxxxxxx>
> Signed-off-by: Mukesh Ojha <quic_mojha@xxxxxxxxxxx>
> ---
>  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 fde33acd46b7..104d86e49b97 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 & mask);
> +
> +	return qcom_scm_io_writel(addr, new);
> +}

I believe this API leaves the atomicity part to the client. or how does
it work?

Thanks,
Pavan