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

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Date:   Thu, 23 Feb 2023 06:14:13 -0800
From:   Bjorn Andersson <andersson@...nel.org>
To:     Mukesh Ojha <quic_mojha@...cinc.com>
Cc:     agross@...nel.org, konrad.dybcio@...aro.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] firmware: scm: Modify only the DLOAD bit in TCSR
 register for download mode

On Tue, Feb 21, 2023 at 08:09:39PM +0530, 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@...cinc.com>
> Signed-off-by: Mukesh Ojha <quic_mojha@...cinc.com>
> ---
>  drivers/firmware/qcom_scm.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/firmware/qcom_scm.c b/drivers/firmware/qcom_scm.c
> index 51eb853..c376ba8 100644
> --- a/drivers/firmware/qcom_scm.c
> +++ b/drivers/firmware/qcom_scm.c
> @@ -419,6 +419,7 @@ static void qcom_scm_set_download_mode(bool enable)
>  {
>  	bool avail;
>  	int ret = 0;
> +	u32 dload_addr_val;
>  
>  	avail = __qcom_scm_is_call_available(__scm->dev,
>  					     QCOM_SCM_SVC_BOOT,
> @@ -426,8 +427,16 @@ 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, &dload_addr_val);
> +		if (ret) {
> +			dev_err(__scm->dev,
> +				"failed to read dload mode address value: %d\n", ret);
> +			return;
> +		}
> +
> +		ret = qcom_scm_io_writel(__scm->dload_mode_addr, enable ?
> +				dload_addr_val | QCOM_SCM_BOOT_SET_DLOAD_MODE :

I prefer to avoid using the ternary operator inside writel, in
particular since you in the next patch mask out the DLOAD_MASK here as
well...

Please make this:

readl();
dload_addr_val  &= ~MASK;
if (enable)
	dload_addr_val |= DLOAD_MODE;
writel();


Also, this is the only "value" we're working on in this function, so
"u32 val" should be sufficient.

Thanks,
Bjorn

> +				dload_addr_val & ~(QCOM_SCM_BOOT_SET_DLOAD_MODE));
>  	} else {
>  		dev_err(__scm->dev,
>  			"No available mechanism for setting download mode\n");
> -- 
> 2.7.4
>