Re: [PATCH v2 1/4] firmware: xilinx: Add sysfs interface

From: Jolly Shah
Date: Thu Jan 30 2020 - 18:59:21 EST


Hi Greg,

ïOn 1/27/20, 10:28 PM, "linux-kernel-owner@xxxxxxxxxxxxxxx on behalf of Greg KH" <linux-kernel-owner@xxxxxxxxxxxxxxx on behalf of gregkh@xxxxxxxxxxxxxxxxxxx> wrote:

On Mon, Jan 27, 2020 at 11:01:27PM +0000, Jolly Shah wrote:
> > > > + ret = kstrtol(tok, 16, &value);
> > > > + if (ret) {
> > > > + ret = -EFAULT;
> > > > + goto err;
> > > > + }
> > > > +
> > > > + ret = eemi_ops->ioctl(0, read_ioctl, reg, 0, ret_payload);
> > >
> > > This feels "tricky", if you tie this to the device you have your driver
> > > bound to, will this make it easier instead of having to go through the
> > > ioctl callback?
> > >
> >
> > GGS(general global storage) registers are in PMU space and linux doesn't have access to it
> > Hence ioctl is used.
>
> Why not just a "real" call to the driver to make this type of reading?
> You don't have ioctls within the kernel for other drivers to call,
> that's not needed at all.
>
> these registers are for users and for special needs where users wants
> to retain values over resets. but as they belong to PMU address space,
> these interface APIs are provided. They donât allow access to any
> other registers.

That's not the issue here. The issue is you are using an "internal"
ioctl, instead just make a "real" call.

Sorry I am not clear. Do you mean that we should use linux standard ioctl interface instead of internal ioctl by mentioning "real" ?

> > > > +int zynqmp_pm_ggs_init(struct kobject *parent_kobj)
> > > > +{
> > > > + return sysfs_create_group(parent_kobj, zynqmp_ggs_groups[0]);
> > >
> > > You might be racing userspace here and loosing :(
> >
> > Prob is called before user space is notified about sysfs so racing shouldn't happen.
>
> "shouldn't"? How do you know this?
>
> Since firmware driver is always built-in (we don't provide support to
> use as module), user space won't be available before prob is complete.
> Correct if I am wrong.

Userspace starts earlier than you think, and also, use the correct
interfaces for this type of thing, that is why it is there. Don't
create purposfully-incorrect code :)

Sure. We will change it.

Thanks,
Jolly Shah


> > > > diff --git a/drivers/firmware/xilinx/zynqmp.c
> > > b/drivers/firmware/xilinx/zynqmp.c
> > > > index 75bdfaa..4c1117d 100644
> > > > --- a/drivers/firmware/xilinx/zynqmp.c
> > > > +++ b/drivers/firmware/xilinx/zynqmp.c
> > > > @@ -473,6 +473,10 @@ static inline int zynqmp_is_valid_ioctl(u32 ioctl_id)
> > > > case IOCTL_GET_PLL_FRAC_MODE:
> > > > case IOCTL_SET_PLL_FRAC_DATA:
> > > > case IOCTL_GET_PLL_FRAC_DATA:
> > > > + case IOCTL_WRITE_GGS:
> > > > + case IOCTL_READ_GGS:
> > > > + case IOCTL_WRITE_PGGS:
> > > > + case IOCTL_READ_PGGS:
> > >
> > > Huh???
> >
> > Sorry not sure about your concern here. These registers are in PMU space and hence
> > Ioctl is needed to let linux access them.
>
> userspace or kernelspace?
>
> You seem to be mixing them both here.
>
> They are in Platform Management Unit register address space so it
> allows only secure access. Hence for linux to access it, interface
> APIs are provided.

Again, that's fine, but why are you creating an "internal ioctl"? Just
make a real function call.

thanks,

greg k-h