Re: [PATCH v2 2/4] firmware: scm: Modify only the DLOAD bit in TCSR register for download mode

[Srinivas Kandagatla <srinivas.kandagatla@linaro.org>]

On 01/03/2023 09:55, Mukesh Ojha wrote:
> CrashDump collection is based on the DLOAD bit of TCSR register.
> To retain other bits, we read the register and modify only the
> DLOAD bit as the other bits have their own significance.
> 
> Originally-by: Poovendhan Selvaraj <quic_poovendh@quicinc.com>
> Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
> ---
> Changes in v2:
>   - Addressed comment made by Bjorn.
>   - Added download mask from patch 3 to this.
> 
>   drivers/firmware/qcom_scm.c | 17 +++++++++++++++--
>   1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/firmware/qcom_scm.c b/drivers/firmware/qcom_scm.c
> index 51eb853..c9f1fad 100644
> --- a/drivers/firmware/qcom_scm.c
> +++ b/drivers/firmware/qcom_scm.c
> @@ -27,6 +27,8 @@ module_param(download_mode, bool, 0);
>   #define SCM_HAS_IFACE_CLK	BIT(1)
>   #define SCM_HAS_BUS_CLK		BIT(2)
>   
> +#define QCOM_DOWNLOAD_MODE_MASK 0x30
> +
>   struct qcom_scm {
>   	struct device *dev;
>   	struct clk *core_clk;
> @@ -419,6 +421,7 @@ static void qcom_scm_set_download_mode(bool enable)
>   {
>   	bool avail;
>   	int ret = 0;
> +	u32 val;
>   
>   	avail = __qcom_scm_is_call_available(__scm->dev,
>   					     QCOM_SCM_SVC_BOOT,
> @@ -426,8 +429,18 @@ static void qcom_scm_set_download_mode(bool enable)
>   	if (avail) {
>   		ret = __qcom_scm_set_dload_mode(__scm->dev, enable);
>   	} else if (__scm->dload_mode_addr) {
> -		ret = qcom_scm_io_writel(__scm->dload_mode_addr,
> -				enable ? QCOM_SCM_BOOT_SET_DLOAD_MODE : 0);
> +		ret = qcom_scm_io_readl(__scm->dload_mode_addr, &val);
> +		if (ret) {
> +			dev_err(__scm->dev,
> +				"failed to read dload mode address value: %d\n", ret);
> +			return;
> +		}
> +
> +		val &= ~QCOM_DOWNLOAD_MODE_MASK;
> +		if (enable)
> +			val |= QCOM_SCM_BOOT_SET_DLOAD_MODE;
> +
> +		ret = qcom_scm_io_writel(__scm->dload_mode_addr, val);


This is the second instance of such pattern of usage one is already in 
./drivers/pinctrl/qcom/pinctrl-msm.c

I think it makes sense to move setting fields in register to a dedicated 
function like this:

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 << ffs(mask) - 1);

	return qcom_scm_io_writel(addr, new);
}
EXPORT_SYMBOL(qcom_scm_io_update_field);


then we could use it like this:
ret = qcom_scm_io_update_field(__scm->dload_mode_addr, 
QCOM_DOWNLOAD_MODE_MASK, dl_mode)


--srini
>   	} else {
>   		dev_err(__scm->dev,
>   			"No available mechanism for setting download mode\n");