Re: [PATCH] soc: qcom: llcc: Add llcc device availability check

[Mukesh Ojha]

On 2/22/2024 11:37 PM, Sahil Chandna wrote:
> On 2/20/2024 5:58 PM, Mukesh Ojha wrote:
> > When llcc driver is enabled  and llcc device is not
> > physically there on the SoC, client can get
> > -EPROBE_DEFER on calling llcc_slice_getd() and it
> > is possible they defer forever.
> >
> > Let's add a check device availabilty and set the
> > appropriate applicable error in drv_data.
> >
> > Signed-off-by: Mukesh Ojha <quic_mojha@xxxxxxxxxxx>
> > ---
> >   drivers/soc/qcom/llcc-qcom.c | 23 ++++++++++++++++++++++-
> >   1 file changed, 22 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/soc/qcom/llcc-qcom.c b/drivers/soc/qcom/llcc-qcom.c
> > index 4ca88eaebf06..cb336b183bba 100644
> > --- a/drivers/soc/qcom/llcc-qcom.c
> > +++ b/drivers/soc/qcom/llcc-qcom.c
> > @@ -769,6 +769,27 @@ static const struct qcom_sct_config x1e80100_cfgs 
> > = {
> >   };
> >   static struct llcc_drv_data *drv_data = (void *) -EPROBE_DEFER;
> > +static DEFINE_MUTEX(dev_avail);
> what is the requirement for mutex lock here? Since we are only trying to 
> find if node present or not

I was trying to avoid two parallel call from llcc_slice_getd() calling
parallel call to of_find_node_by_name() as it should be one time search 
for device presence to find a node and check if device is present or
not.

-Mukesh

> > +
> > +static bool is_llcc_device_available(void)
> > +{
> > +    static struct llcc_drv_data *ptr;
> > +
> > +    mutex_lock(&dev_avail);
> > +    if (!ptr) {
> > +        struct device_node *node;
> > +
> > +        node = of_find_node_by_name(NULL, "system-cache-controller");
> > +        if (!of_device_is_available(node)) {
> > +            pr_warn("llcc-qcom: system-cache-controller node not 
> > found\n");
> > +            drv_data = ERR_PTR(-ENODEV);
> > +        }
> > +        of_node_put(node);
> > +        ptr = drv_data;
> > +    }
> > +    mutex_unlock(&dev_avail);
> > +    return (PTR_ERR(ptr) != -ENODEV) ? true : false;
> > +}
> >   /**
> >    * llcc_slice_getd - get llcc slice descriptor
> > @@ -783,7 +804,7 @@ struct llcc_slice_desc *llcc_slice_getd(u32 uid)
> >       struct llcc_slice_desc *desc;
> >       u32 sz, count;
> > -    if (IS_ERR(drv_data))
> > +    if (!is_llcc_device_available() || IS_ERR(drv_data))
> >           return ERR_CAST(drv_data);
> >       cfg = drv_data->cfg;