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

[Sahil Chandna]

On 2/26/2024 4:02 PM, Mukesh Ojha wrote:
> 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
Got it, but of_find_node_by_name () is holding a raw_spin_lock_irqsave 
() for concurrency, right ? please correct me if understanding is wrong.
> > > +
> > > +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))
Also, thinking about this, should the status of device present or not be 
saved in static variable instead of function call for each client ?
> > >           return ERR_CAST(drv_data);
> > >       cfg = drv_data->cfg;

Regards,
Sahil