[Intel-gfx] [PATCH v4 05/13] drivers: create binary sysfs for class
gregkh at linuxfoundation.org
Mon Apr 15 18:01:40 UTC 2019
On Mon, Apr 15, 2019 at 10:44:12PM +0530, Ramalingam C wrote:
> On 2019-04-15 at 16:47:16 +0200, Greg Kroah-Hartman wrote:
> > On Mon, Apr 15, 2019 at 06:11:13PM +0530, Ramalingam C wrote:
> > > 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.
> > > Greg,
> > >
> > > 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.
> > Again, the kernel is NOT to be parsing any binary data that comes
> > through a sysfs file. If you need such a crazy thing, do it through
> > your normal drm ioctl.
> > > 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?
> > What is a "cardx" driver?
> Meant card0 card1 etc.. Drm drivers.
> > Why can you not do it in a device-specific
> > location? Are suddenly _ALL_ DRM drivers going to need this
> > information? What is the use case? Who is going to be providing this
> > blob and where is it going? What in the kernel uses it? What on the
> > hardware uses it? What is it actually?
> This is for HDCP usecase. List of compromised receivers' ID called system
> renewability Message (SRM) will be available at userspace which needs to
> be passed to be kernel. And this data can be parsed at kernel used
> across all DRM drivers to implement the HDCP authentication. Hence we
> want generic code to parse the SRM data and provide a helper function to
> all DRM drivers to validate their HDCP sink's ID.
> To achieve this we want to keep the sysfs and parsing logic outside the
> drm drivers at the class level.
> At present I915 will be using these implementation. in future other DRM
> drivers can use the same.
Again, binary sysfs files are not for any data that the kernel has to
parse at all. So do not use sysfs for this.
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