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

Bjorn Andersson
2023-03-27T18:20:23Z

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