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

[Mukesh Ojha <quic_mojha@xxxxxxxxxxx>]

On 3/27/2023 11:53 PM, Bjorn Andersson wrote:
> 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.


If we use strcmp, i need to use "full\n" which we would not want to do.
I think, we need to take this hit.

-- Mukesh
> > +		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