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

[Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>]

On 28/03/2023 11:18, Mukesh Ojha wrote:
> 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.

There is a special helper for the sysfs files. See sysfs_streq().

> -- 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

--
With best wishes
Dmitry