Re: [PATCH v11 1/4] firmware: qcom: scm: provide a read-modify-write function

[Bjorn Andersson <andersson@xxxxxxxxxx>]

On Mon, Jan 08, 2024 at 08:57:31PM +0530, Mukesh Ojha wrote:
> It was realized by Srinivas K. that there is a need of

"need" is a strong word for this functionality, unless there's some use
case that I'm missing.

> read-modify-write scm exported function so that it can
> be used by multiple clients.
> 
> Let's introduce qcom_scm_io_rmw() which masks out the bits
> and write the passed value to that bit-offset.
> 
> Suggested-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
> Signed-off-by: Mukesh Ojha <quic_mojha@xxxxxxxxxxx>
> Tested-by: Kathiravan Thirumoorthy <quic_kathirav@xxxxxxxxxxx> # IPQ9574 and IPQ5332
> ---
>  drivers/firmware/qcom/qcom_scm.c       | 26 ++++++++++++++++++++++++++
>  include/linux/firmware/qcom/qcom_scm.h |  1 +
>  2 files changed, 27 insertions(+)
> 
> diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
> index 520de9b5633a..25549178a30f 100644
> --- a/drivers/firmware/qcom/qcom_scm.c
> +++ b/drivers/firmware/qcom/qcom_scm.c
> @@ -19,6 +19,7 @@
>  #include <linux/of_irq.h>
>  #include <linux/of_platform.h>
>  #include <linux/platform_device.h>
> +#include <linux/spinlock.h>
>  #include <linux/reset-controller.h>
>  #include <linux/types.h>
>  
> @@ -41,6 +42,8 @@ struct qcom_scm {
>  	int scm_vote_count;
>  
>  	u64 dload_mode_addr;
> +	/* Atomic context only */
> +	spinlock_t lock;
>  };
>  
>  struct qcom_scm_current_perm_info {
> @@ -481,6 +484,28 @@ static int qcom_scm_disable_sdi(void)
>  	return ret ? : res.result[0];
>  }
>  
> +int qcom_scm_io_rmw(phys_addr_t addr, unsigned int mask, unsigned int val)
> +{
> +	unsigned int old, new;
> +	int ret;
> +
> +	if (!__scm)
> +		return -EINVAL;
> +
> +	spin_lock(&__scm->lock);

Please express that this lock is just for create mutual exclusion
between rmw operations, nothing else.

Also please make a statement why this is desirable and/or needed.

Regards,
Bjorn

> +	ret = qcom_scm_io_readl(addr, &old);
> +	if (ret)
> +		goto unlock;
> +
> +	new = (old & ~mask) | (val & mask);
> +
> +	ret = qcom_scm_io_writel(addr, new);
> +unlock:
> +	spin_unlock(&__scm->lock);
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(qcom_scm_io_rmw);
> +
>  static int __qcom_scm_set_dload_mode(struct device *dev, bool enable)
>  {
>  	struct qcom_scm_desc desc = {
> @@ -1824,6 +1849,7 @@ static int qcom_scm_probe(struct platform_device *pdev)
>  		return ret;
>  
>  	mutex_init(&scm->scm_bw_lock);
> +	spin_lock_init(&scm->lock);
>  
>  	scm->path = devm_of_icc_get(&pdev->dev, NULL);
>  	if (IS_ERR(scm->path))
> diff --git a/include/linux/firmware/qcom/qcom_scm.h b/include/linux/firmware/qcom/qcom_scm.h
> index ccaf28846054..3a8bb2e603b3 100644
> --- a/include/linux/firmware/qcom/qcom_scm.h
> +++ b/include/linux/firmware/qcom/qcom_scm.h
> @@ -82,6 +82,7 @@ bool qcom_scm_pas_supported(u32 peripheral);
>  
>  int qcom_scm_io_readl(phys_addr_t addr, unsigned int *val);
>  int qcom_scm_io_writel(phys_addr_t addr, unsigned int val);
> +int qcom_scm_io_rmw(phys_addr_t addr, unsigned int mask, unsigned int val);
>  
>  bool qcom_scm_restore_sec_cfg_available(void);
>  int qcom_scm_restore_sec_cfg(u32 device_id, u32 spare);
> -- 
> 2.7.4
>