linux-kernel - Re: [PATCH v4 4/5] firmware: qcom_scm: Refactor code to support multiple download mode

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Message-ID: <20230327182324.elrxciz5vqvryp7y@ripper>
Date:   Mon, 27 Mar 2023 11:23:24 -0700
From:   Bjorn Andersson <andersson@...nel.org>
To:     Mukesh Ojha <quic_mojha@...cinc.com>
Cc:     agross@...nel.org, konrad.dybcio@...aro.org,
        linus.walleij@...aro.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org
Subject: Re: [PATCH v4 4/5] firmware: qcom_scm: Refactor code to support
 multiple download mode

On Mon, Mar 27, 2023 at 10:11:20PM +0530, Mukesh Ojha wrote:
[..]
> diff --git a/drivers/firmware/qcom_scm.c b/drivers/firmware/qcom_scm.c
> index 3c6c5e7..0c94429 100644
> --- a/drivers/firmware/qcom_scm.c
> +++ b/drivers/firmware/qcom_scm.c
> @@ -20,11 +20,11 @@
>  #include <linux/clk.h>
>  #include <linux/reset-controller.h>
>  #include <linux/arm-smccc.h>
> +#include <linux/kstrtox.h>
>  
>  #include "qcom_scm.h"
>  
> -static bool download_mode = IS_ENABLED(CONFIG_QCOM_SCM_DOWNLOAD_MODE_DEFAULT);
> -module_param(download_mode, bool, 0);
> +static u32 download_mode;
>  
>  #define SCM_HAS_CORE_CLK	BIT(0)
>  #define SCM_HAS_IFACE_CLK	BIT(1)
> @@ -32,6 +32,7 @@ module_param(download_mode, bool, 0);
>  
>  #define QCOM_DOWNLOAD_MODE_MASK 0x30
>  #define QCOM_DOWNLOAD_FULLDUMP	0x1
> +#define QCOM_DOWNLOAD_NODUMP	0x0
>  
>  struct qcom_scm {
>  	struct device *dev;
> @@ -440,8 +441,9 @@ static int __qcom_scm_set_dload_mode(struct device *dev, bool enable)
>  	return qcom_scm_call_atomic(__scm->dev, &desc, NULL);
>  }
>  
> -static void qcom_scm_set_download_mode(bool enable)
> +static void qcom_scm_set_download_mode(u32 download_mode)
>  {
> +	bool enable = !!download_mode;
>  	bool avail;
>  	int ret = 0;
>  
> @@ -453,7 +455,7 @@ static void qcom_scm_set_download_mode(bool enable)
>  	} else if (__scm->dload_mode_addr) {
>  		ret = qcom_scm_io_update_field(__scm->dload_mode_addr,
>  				QCOM_DOWNLOAD_MODE_MASK,
> -				enable ? QCOM_DOWNLOAD_FULLDUMP : 0);
> +				enable ? download_mode : 0);

Afaict, with QCOM_DOWNLOAD_NODUMP as 0, this says:

  when download_mode is non-zero, write that value, otherwise write 0

That should be the same as "write download_mode", so you should be able
to drop the enable part.

>  	} else {
>  		dev_err(__scm->dev,
>  			"No available mechanism for setting download mode\n");
> @@ -1419,6 +1421,49 @@ static irqreturn_t qcom_scm_irq_handler(int irq, void *data)
>  	return IRQ_HANDLED;
>  }
>  
> +
> +static int get_download_mode(char *buffer, const struct kernel_param *kp)
> +{
> +	int len = 0;
> +
> +	if (download_mode == QCOM_DOWNLOAD_FULLDUMP)
> +		len = sysfs_emit(buffer, "full\n");
> +	else if (download_mode == QCOM_DOWNLOAD_NODUMP)
> +		len = sysfs_emit(buffer, "off\n");
> +
> +	return len;
> +}
> +
> +static int set_download_mode(const char *val, const struct kernel_param *kp)
> +{
> +	u32 old = download_mode;
> +
> +	if (!strncmp(val, "full", strlen("full"))) {

strcmp loops over the two string until they differ and/or both are
'\0'.

As such, the only thing you achieve by using strncmp(.., T, strlen(T))
is that the code has to iterate over T twice - and you make the code
harder to read.

> +		download_mode = QCOM_DOWNLOAD_FULLDUMP;
> +	} else if (!strncmp(val, "off", strlen("off"))) {
> +		download_mode = QCOM_DOWNLOAD_NODUMP;
> +	} else if (kstrtouint(val, 0, &download_mode) ||
> +		   !(download_mode == 0 || download_mode == 1)) {
> +		download_mode = old;
> +		pr_err("unknown download mode\n");

This will result in a lone "unknown download mode" line somewhere in the
kernel log, without association to any driver or any indication what the
unknown value was.

  pr_err("qcom_scm: unknown download mode: %s\n", val);

Would give both context and let the reader know right there what value
the code wasn't able to match.

Regards,
Bjorn