Re: [PATCH v2 2/4] firmware: scm: Modify only the DLOAD bit in TCSR register for download mode

[Mukesh Ojha]

On 3/1/2023 4:09 PM, Dmitry Baryshkov wrote:
> On 01/03/2023 11:55, Mukesh Ojha wrote:
> > CrashDump collection is based on the DLOAD bit of TCSR register.
> > To retain other bits, we read the register and modify only the
> > DLOAD bit as the other bits have their own significance.
> >
> > Originally-by: Poovendhan Selvaraj <quic_poovendh@xxxxxxxxxxx>
> > Signed-off-by: Mukesh Ojha <quic_mojha@xxxxxxxxxxx>
> > ---
> > Changes in v2:
> >   - Addressed comment made by Bjorn.
> >   - Added download mask from patch 3 to this.
> >
> >   drivers/firmware/qcom_scm.c | 17 +++++++++++++++--
> >   1 file changed, 15 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/firmware/qcom_scm.c b/drivers/firmware/qcom_scm.c
> > index 51eb853..c9f1fad 100644
> > --- a/drivers/firmware/qcom_scm.c
> > +++ b/drivers/firmware/qcom_scm.c
> > @@ -27,6 +27,8 @@ module_param(download_mode, bool, 0);
> >   #define SCM_HAS_IFACE_CLK    BIT(1)
> >   #define SCM_HAS_BUS_CLK        BIT(2)
> > +#define QCOM_DOWNLOAD_MODE_MASK 0x30
> > +
> >   struct qcom_scm {
> >       struct device *dev;
> >       struct clk *core_clk;
> > @@ -419,6 +421,7 @@ static void qcom_scm_set_download_mode(bool enable)
> >   {
> >       bool avail;
> >       int ret = 0;
> > +    u32 val;
> >       avail = __qcom_scm_is_call_available(__scm->dev,
> >                            QCOM_SCM_SVC_BOOT,
> > @@ -426,8 +429,18 @@ static void qcom_scm_set_download_mode(bool enable)
> >       if (avail) {
> >           ret = __qcom_scm_set_dload_mode(__scm->dev, enable);
> >       } else if (__scm->dload_mode_addr) {
> > -        ret = qcom_scm_io_writel(__scm->dload_mode_addr,
> > -                enable ? QCOM_SCM_BOOT_SET_DLOAD_MODE : 0);
> > +        ret = qcom_scm_io_readl(__scm->dload_mode_addr, &val);
> > +        if (ret) {
> > +            dev_err(__scm->dev,
> > +                "failed to read dload mode address value: %d\n", ret);
> > +            return;
> > +        }
> > +
> > +        val &= ~QCOM_DOWNLOAD_MODE_MASK;
> > +        if (enable)
> > +            val |= QCOM_SCM_BOOT_SET_DLOAD_MODE;
> > +
> > +        ret = qcom_scm_io_writel(__scm->dload_mode_addr, val);
>
> Any locking for this RMW?

While you ask this, i thought about who all are the user of this 
function. Only, multiple calls to module param callback where
this race could be possible.

I am doubtful, if introducing global mutex lock will be allowed to 
handle this. Any comments.


-Mukesh
> >       } else {
> >           dev_err(__scm->dev,
> >               "No available mechanism for setting download mode\n");