Re: [PATCH v2 3/4] firmware: qcom_scm: Refactor code to support multiple download mode

[Dmitry Baryshkov]

On 01/03/2023 11:55, Mukesh Ojha wrote:
> Currently on Qualcomm SoC, download_mode is enabled if
> CONFIG_QCOM_SCM_DOWNLOAD_MODE_DEFAULT is selected.
>
> Refactor the code such that it supports multiple download
> modes and drop CONFIG_QCOM_SCM_DOWNLOAD_MODE_DEFAULT config
> instead, give interface to set the download mode from
> module parameter.
>
> Signed-off-by: Mukesh Ojha <quic_mojha@xxxxxxxxxxx>
> ---
> Changes in v2:
>   - Passed download mode as parameter
>   - Accept human accepatable download mode string.
>   - enable = !!dload_mode
>   - Shifted module param callback to somewhere down in
>     the file so that it no longer need to know the
>     prototype of qcom_scm_set_download_mode()
>   - updated commit text.
>
>   drivers/firmware/Kconfig    | 11 --------
>   drivers/firmware/qcom_scm.c | 65 ++++++++++++++++++++++++++++++++++++++-------
>   2 files changed, 56 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
> index b59e304..ff7e9f3 100644
> --- a/drivers/firmware/Kconfig
> +++ b/drivers/firmware/Kconfig
> @@ -215,17 +215,6 @@ config MTK_ADSP_IPC
>   config QCOM_SCM
>   	tristate
>   
> -config QCOM_SCM_DOWNLOAD_MODE_DEFAULT
> -	bool "Qualcomm download mode enabled by default"
> -	depends on QCOM_SCM
> -	help
> -	  A device with "download mode" enabled will upon an unexpected
> -	  warm-restart enter a special debug mode that allows the user to
> -	  "download" memory content over USB for offline postmortem analysis.
> -	  The feature can be enabled/disabled on the kernel command line.
> -
> -	  Say Y here to enable "download mode" by default.
> -
>   config SYSFB
>   	bool
>   	select BOOT_VESA_SUPPORT
> diff --git a/drivers/firmware/qcom_scm.c b/drivers/firmware/qcom_scm.c
> index c9f1fad..ca07208 100644
> --- a/drivers/firmware/qcom_scm.c
> +++ b/drivers/firmware/qcom_scm.c
> @@ -17,17 +17,22 @@
>   #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);
> -
>   #define SCM_HAS_CORE_CLK	BIT(0)
>   #define SCM_HAS_IFACE_CLK	BIT(1)
>   #define SCM_HAS_BUS_CLK		BIT(2)
>   
>   #define QCOM_DOWNLOAD_MODE_MASK 0x30
> +#define QCOM_DOWNLOAD_FULLDUMP	0x10
> +#define QCOM_DOWNLOAD_NODUMP	0x0
> +
> +#define MAX_DLOAD_LEN	8
> +
> +static char download_mode[] = "off";
> +static u32 dload_mode;
>   
>   struct qcom_scm {
>   	struct device *dev;
> @@ -417,8 +422,9 @@ 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 dload_mode)
>   {
> +	bool enable = !!dload_mode;
>   	bool avail;
>   	int ret = 0;
>   	u32 val;
> @@ -438,7 +444,7 @@ static void qcom_scm_set_download_mode(bool enable)
>   
>   		val &= ~QCOM_DOWNLOAD_MODE_MASK;
>   		if (enable)
> -			val |= QCOM_SCM_BOOT_SET_DLOAD_MODE;
> +			val |= dload_mode;
>   
>   		ret = qcom_scm_io_writel(__scm->dload_mode_addr, val);
>   	} else {
> @@ -1338,6 +1344,47 @@ bool qcom_scm_is_available(void)
>   }
>   EXPORT_SYMBOL(qcom_scm_is_available);
>   
> +static int set_dload_mode(const char *val, const struct kernel_param *kp)
> +{
> +	int ret;
> +
> +	if (!strncmp(val, "full", strlen("full"))) {
> +		dload_mode = QCOM_DOWNLOAD_FULLDUMP;
> +	} else if (!strncmp(val, "off", strlen("off"))) {
> +		dload_mode = QCOM_DOWNLOAD_NODUMP;
> +	} else {
> +		if (kstrtouint(val, 0, &dload_mode) ||
> +		     !(dload_mode == 0 || dload_mode == 1)) {
> +			pr_err("unknown download mode\n");
> +			return -EINVAL;
> +		}
> +
> +	}
> +
> +	ret = param_set_copystring(val, kp);
> +	if (ret)
> +		return ret;
> +
> +	if (__scm)
> +		qcom_scm_set_download_mode(dload_mode);
> +
> +	return 0;
> +}
> +
> +static const struct kernel_param_ops dload_mode_param_ops = {
> +	.set = set_dload_mode,
> +	.get = param_get_string,

Please follow the param_get_bool approach and return sanitized data 
here. In other words, "full" / "none" depending on the dload_mode 
instead of storing the passed string and returning it later.

> +};
> +
> +static struct kparam_string dload_mode_param = {
> +	.string = download_mode,
> +	.maxlen = MAX_DLOAD_LEN,

I think writing "full" to this param might overwrite some kernel data. 
"00000000" should be even worse.

> +};
> +
> +module_param_cb(download_mode, &dload_mode_param_ops, &dload_mode_param, 0644);
> +MODULE_PARM_DESC(download_mode,
> +		 "Download mode: off/full or 0/1/off/on for existing users");

Nit: on is not supported even for existing users.

> +
>   static int qcom_scm_probe(struct platform_device *pdev)
>   {
>   	struct qcom_scm *scm;
> @@ -1418,12 +1465,12 @@ static int qcom_scm_probe(struct platform_device *pdev)
>   	__get_convention();
>   
>   	/*
> -	 * If requested enable "download mode", from this point on warmboot
> +	 * If download mode is requested, from this point on warmboot
>   	 * will cause the boot stages to enter download mode, unless
>   	 * disabled below by a clean shutdown/reboot.
>   	 */
> -	if (download_mode)
> -		qcom_scm_set_download_mode(true);
> +	if (dload_mode)
> +		qcom_scm_set_download_mode(dload_mode);
>   
>   	return 0;
>   }
> @@ -1431,7 +1478,7 @@ static int qcom_scm_probe(struct platform_device *pdev)
>   static void qcom_scm_shutdown(struct platform_device *pdev)
>   {
>   	/* Clean shutdown, disable download mode to allow normal restart */
> -	qcom_scm_set_download_mode(false);
> +	qcom_scm_set_download_mode(QCOM_DOWNLOAD_NODUMP);
>   }
>   
>   static const struct of_device_id qcom_scm_dt_match[] = {

--
With best wishes
Dmitry