[Intel-gfx] [PATCH v4 05/13] drivers: create binary sysfs for class

Ramalingam C ramalingam.c at intel.com
Mon Apr 15 12:41:13 UTC 2019

On 2019-04-05 at 14:32:00 +0200, Greg Kroah-Hartman wrote:
> On Fri, Apr 05, 2019 at 04:06:22PM +0530, Ramalingam C wrote:
> > On 2019-04-05 at 11:23:00 +0200, Greg Kroah-Hartman wrote:
> > > On Fri, Apr 05, 2019 at 02:12:54PM +0530, Ramalingam C wrote:
> > > > Functions to create and remove the binary sysfs for class are added.
> > > > 
> > > > These are getting introduced as DRM wants to create the common binary
> > > > sysfs across the drm subsystem to handle hdcp srm.
> > > 
> > > Why do you need individual files?  That's almost always a sign that you
> > > are going to race with userspace in a bad way.  Why not just use an
> > > attribute group which provides automatic support for this?
> > Greg,
> > 
> > Reason behind this move is to have a common srm entry path across all drm
> > drivers. And the data fed into this is binary blob. So I am creating a
> > binary sysfs "hdcp_srm" at /sys/class/drm/
> Ah, you want to have a file in your class directory, not your class
> device directory.
> No, please do not do that.  There's a reason I got rid of those same
> types of apis in the past.
> And "binary blobs" are horrid anyway, they are only to be used as a
> pass-through to the device itself, from the kernel, no touching the data
> at all.  If you really need/want this, then put it in the device's
> directory as that is where the data is going to, not the kernel "class"
> code as it sure as heck better not be doing anything with it.

But here the parsing of the received binary blob is done outside the drm
device/cards. This will be generic code for all drm cardx(drivers). And
this will provide the service helper functions to the drm drivers for HDCP SRM checking.

So we prefer to have the binary sysfs at /sys/class/drm/ than inside the
cardx folders, so that it will be generic. Could you please suggest a way to achieve that?

> thanks,
> greg k-h

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