Re: [PATCH 9/9] drm/simplekms: Acquire memory aperture for framebuffer

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Jun 29, 2020 at 08:13:51PM -0600, Rob Herring wrote:
> On Mon, Jun 29, 2020 at 10:04 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> >
> > On Mon, Jun 29, 2020 at 11:22:30AM +0200, Daniel Vetter wrote:
> > > On Thu, Jun 25, 2020 at 02:00:11PM +0200, Thomas Zimmermann wrote:
> > > > We register the simplekms device with the DRM platform helpers. A
> > > > native driver for the graphics hardware will kickout the simplekms
> > > > driver before taking over the device.
> > > >
> > > > Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> > > > ---
> > > >  drivers/gpu/drm/tiny/Kconfig     |  1 +
> > > >  drivers/gpu/drm/tiny/simplekms.c | 94 +++++++++++++++++++++++++++++++-
> > > >  2 files changed, 92 insertions(+), 3 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/tiny/Kconfig b/drivers/gpu/drm/tiny/Kconfig
> > > > index 50dbde8bdcb2..a47ed337a7fe 100644
> > > > --- a/drivers/gpu/drm/tiny/Kconfig
> > > > +++ b/drivers/gpu/drm/tiny/Kconfig
> > > > @@ -33,6 +33,7 @@ config DRM_SIMPLEKMS
> > > >     depends on DRM
> > > >     select DRM_GEM_SHMEM_HELPER
> > > >     select DRM_KMS_HELPER
> > > > +   select DRM_PLATFORM_HELPER
> > > >     help
> > > >       DRM driver for simple platform-provided framebuffers.
> > > >
> > > > diff --git a/drivers/gpu/drm/tiny/simplekms.c b/drivers/gpu/drm/tiny/simplekms.c
> > > > index ae5d3cbadbe8..a903a4e0100a 100644
> > > > --- a/drivers/gpu/drm/tiny/simplekms.c
> > > > +++ b/drivers/gpu/drm/tiny/simplekms.c
> > > > @@ -5,6 +5,7 @@
> > > >  #include <linux/platform_data/simplefb.h>
> > > >  #include <linux/platform_device.h>
> > > >  #include <linux/regulator/consumer.h>
> > > > +#include <linux/spinlock.h>
> > > >
> > > >  #include <drm/drm_atomic_state_helper.h>
> > > >  #include <drm/drm_connector.h>
> > > > @@ -17,6 +18,7 @@
> > > >  #include <drm/drm_gem_shmem_helper.h>
> > > >  #include <drm/drm_managed.h>
> > > >  #include <drm/drm_modeset_helper_vtables.h>
> > > > +#include <drm/drm_platform.h>
> > > >  #include <drm/drm_probe_helper.h>
> > > >  #include <drm/drm_simple_kms_helper.h>
> > > >
> > > > @@ -36,6 +38,12 @@
> > > >  #define SIMPLEKMS_MODE(hd, vd)     \
> > > >     DRM_SIMPLE_MODE(hd, vd, RES_MM(hd), RES_MM(vd))
> > > >
> > > > +/*
> > > > + * Protects the platform device's drvdata against
> > > > + * concurrent manipulation.
> > > > + */
> > > > +static DEFINE_SPINLOCK(simplekms_drvdata_lock);
> > > > +
> > > >  /*
> > > >   * Helpers for simplefb
> > > >   */
> > > > @@ -211,6 +219,7 @@ struct simplekms_device {
> > > >     unsigned int pitch;
> > > >
> > > >     /* memory management */
> > > > +   struct drm_aperture *aperture;
> > > >     struct resource *mem;
> > > >     void __iomem *screen_base;
> > > >
> > > > @@ -224,6 +233,8 @@ static struct simplekms_device *simplekms_device_of_dev(struct drm_device *dev)
> > > >     return container_of(dev, struct simplekms_device, dev);
> > > >  }
> > > >
> > > > +static void simplekms_device_cleanup(struct simplekms_device *sdev);
> > > > +
> > > >  /*
> > > >   * Hardware
> > > >   */
> > > > @@ -514,22 +525,72 @@ static int simplekms_device_init_fb(struct simplekms_device *sdev)
> > > >   * Memory management
> > > >   */
> > > >
> > > > +static void simplekms_aperture_kickout(struct drm_aperture *ap)
> > > > +{
> > > > +   struct drm_device *dev = ap->dev;
> > > > +   struct simplekms_device *sdev = simplekms_device_of_dev(dev);
> > > > +   struct platform_device *pdev = sdev->pdev;
> > > > +
> > > > +   if (WARN_ON(!sdev->aperture))
> > > > +           return; /* BUG: driver already got kicked out */
> > > > +
> > > > +   drm_dev_unregister(dev);
> > >
> > > >From a semantic pov I think the platform driver getting kicked out is more
> > > like a hotunplug, so drm_dev_unplug(dev); here is imo better.
> > >
> > > That then also gives you a nice drm_dev_enter/exit to sprinkle over the
> > > various driver callbacks, instead of the racy ->aperture check reinvented
> > > wheel here.
> > >
> > > I also wonder whether we couldn't go full driver model for these platform
> > > devices, and instead of this here call a core driver model function to
> > > force the unbding of the driver. Only change we'd need it that our
> > > ->remove hook uses drm_dev_unplug().
> >
> > Yes, please do that.  Or, use the "virtual bus/device" code that some
> > people at Intel are still trying to get into mergable shape.  See the
> > posts on the netdev list for those details.
> >
> > Don't use platform devices for anything that is not actually a platform
> > device (i.e. something described by hardware resources).
> 
> Well, 'simple-framebuffer' is described by DT and includes h/w
> resources such as clocks. So this is a gray area. I'm not saying we
> couldn't use virtual bus for DT nodes, but we'll need some clear
> guidelines of when to use virtual vs. platform devices. No doubt I'll
> get a 'virtual bus' binding if folks are directed to make things a
> virtual device.

If it is described by DT, then I have no objection for it to be a
platform device.

thanks,

greg k-h
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