Re: [PATCH 2/2] drm/mgag200: Add vblank support

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Sep 11, 2019 at 05:08:45PM +0200, Thomas Zimmermann wrote:
> Hi
> 
> Am 10.09.19 um 16:01 schrieb Ville Syrjälä:
> > On Mon, Sep 09, 2019 at 04:06:33PM +0200, Thomas Zimmermann wrote:
> >> Support for vblank requires VSYNC to signal an interrupt, which is broken
> >> on Matrox chipsets.
> > 
> > I don't remember there being anything wrong with the vsync interrupt.
> > What makes you think it's broken?
> > 
> >> The workaround that is used here and in other free
> >> Matrox drivers is to program <linecomp> to the value of <vdisplay> and
> >> enable the VLINE interrupt. This triggers an interrupt at the same time
> >> when VSYNC begins.
> > 
> > You're programming it to fire at start of vblank, not start of vsync.
> > 
> >>
> >> VLINE uses separate registers for enabling and clearing pending interrupts.
> >> No extra syncronization between irq handler and the rest of the driver is
> >> required.
> >>
> >> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> >> ---
> >>  drivers/gpu/drm/mgag200/mgag200_drv.c  |  1 +
> >>  drivers/gpu/drm/mgag200/mgag200_drv.h  |  1 +
> >>  drivers/gpu/drm/mgag200/mgag200_main.c | 33 ++++++++++++++++++++
> >>  drivers/gpu/drm/mgag200/mgag200_mode.c | 42 +++++++++++++++++++++++---
> >>  4 files changed, 73 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/mgag200/mgag200_drv.c b/drivers/gpu/drm/mgag200/mgag200_drv.c
> >> index 4f9df3b93598..cff265973154 100644
> >> --- a/drivers/gpu/drm/mgag200/mgag200_drv.c
> >> +++ b/drivers/gpu/drm/mgag200/mgag200_drv.c
> >> @@ -67,6 +67,7 @@ static struct drm_driver driver = {
> >>  	.driver_features = DRIVER_GEM | DRIVER_MODESET,
> >>  	.load = mgag200_driver_load,
> >>  	.unload = mgag200_driver_unload,
> >> +	.irq_handler = mgag200_irq_handler,
> >>  	.fops = &mgag200_driver_fops,
> >>  	.name = DRIVER_NAME,
> >>  	.desc = DRIVER_DESC,
> >> diff --git a/drivers/gpu/drm/mgag200/mgag200_drv.h b/drivers/gpu/drm/mgag200/mgag200_drv.h
> >> index 1c93f8dc08c7..88cf256d135f 100644
> >> --- a/drivers/gpu/drm/mgag200/mgag200_drv.h
> >> +++ b/drivers/gpu/drm/mgag200/mgag200_drv.h
> >> @@ -195,6 +195,7 @@ void mgag200_modeset_fini(struct mga_device *mdev);
> >>  				/* mgag200_main.c */
> >>  int mgag200_driver_load(struct drm_device *dev, unsigned long flags);
> >>  void mgag200_driver_unload(struct drm_device *dev);
> >> +irqreturn_t mgag200_irq_handler(int irq, void *arg);
> >>  
> >>  				/* mgag200_i2c.c */
> >>  struct mga_i2c_chan *mgag200_i2c_create(struct drm_device *dev);
> >> diff --git a/drivers/gpu/drm/mgag200/mgag200_main.c b/drivers/gpu/drm/mgag200/mgag200_main.c
> >> index a9773334dedf..5941607796e8 100644
> >> --- a/drivers/gpu/drm/mgag200/mgag200_main.c
> >> +++ b/drivers/gpu/drm/mgag200/mgag200_main.c
> >> @@ -10,7 +10,9 @@
> >>  
> >>  #include <drm/drm_crtc_helper.h>
> >>  #include <drm/drm_gem_framebuffer_helper.h>
> >> +#include <drm/drm_irq.h>
> >>  #include <drm/drm_pci.h>
> >> +#include <drm/drm_vblank.h>
> >>  
> >>  #include "mgag200_drv.h"
> >>  
> >> @@ -186,10 +188,18 @@ int mgag200_driver_load(struct drm_device *dev, unsigned long flags)
> >>  	}
> >>  	mdev->cursor.pixels_current = NULL;
> >>  
> >> +	r = drm_vblank_init(dev, 1);
> >> +	if (r)
> >> +		goto err_modeset;
> >> +
> >>  	r = drm_fbdev_generic_setup(mdev->dev, 0);
> >>  	if (r)
> >>  		goto err_modeset;
> >>  
> >> +	r = drm_irq_install(dev, dev->pdev->irq);
> >> +	if (r)
> >> +		goto err_modeset;
> >> +
> >>  	return 0;
> >>  
> >>  err_modeset:
> >> @@ -207,8 +217,31 @@ void mgag200_driver_unload(struct drm_device *dev)
> >>  
> >>  	if (mdev == NULL)
> >>  		return;
> >> +	drm_irq_uninstall(dev);
> >>  	mgag200_modeset_fini(mdev);
> >>  	drm_mode_config_cleanup(dev);
> >>  	mgag200_mm_fini(mdev);
> >>  	dev->dev_private = NULL;
> >>  }
> >> +
> >> +irqreturn_t mgag200_irq_handler(int irq, void *arg)
> >> +{
> >> +	struct drm_device *dev = arg;
> >> +	struct mga_device *mdev = dev->dev_private;
> >> +	struct drm_crtc *crtc;
> >> +	u32 status, iclear;
> >> +
> >> +	status = RREG32(0x1e14);
> >> +
> >> +	if (status & 0x00000020) { /* test <vlinepen> */
> >> +		drm_for_each_crtc(crtc, dev) {
> >> +			drm_crtc_handle_vblank(crtc);
> >> +		}
> > 
> > A bit odd way to write that but as long this driver doesn't support
> > crtc2 it should be fine.
> > 
> >> +		iclear = RREG32(0x1e18);
> >> +		iclear |= 0x00000020; /* set <vlineiclr> */
> >> +		WREG32(0x1e18, iclear);
> >> +		return IRQ_HANDLED;
> >> +	}
> >> +
> >> +	return IRQ_NONE;
> >> +};
> >> diff --git a/drivers/gpu/drm/mgag200/mgag200_mode.c b/drivers/gpu/drm/mgag200/mgag200_mode.c
> >> index 5e778b5f1a10..ffe5f15d0a7d 100644
> >> --- a/drivers/gpu/drm/mgag200/mgag200_mode.c
> >> +++ b/drivers/gpu/drm/mgag200/mgag200_mode.c
> >> @@ -905,6 +905,7 @@ static int mga_crtc_mode_set(struct drm_crtc *crtc,
> >>  	const struct drm_framebuffer *fb = crtc->primary->fb;
> >>  	int hdisplay, hsyncstart, hsyncend, htotal;
> >>  	int vdisplay, vsyncstart, vsyncend, vtotal;
> >> +	int linecomp;
> >>  	int pitch;
> >>  	int option = 0, option2 = 0;
> >>  	int i;
> >> @@ -1042,6 +1043,13 @@ static int mga_crtc_mode_set(struct drm_crtc *crtc,
> >>  	vsyncend = mode->vsync_end - 1;
> >>  	vtotal = mode->vtotal - 2;
> >>  
> >> +	/* The VSYNC interrupt is broken on Matrox chipsets. We use
> >> +	 * the VLINE interrupt instead. It triggers when the current
> >> +	 * linecomp has been reached. Therefore keep <linecomp> in
> >> +	 * sync with <vdisplay>.
> >> +	 */
> >> +	linecomp = vdisplay;
> > 
> > I have an odd recollection that you want vdisplay+1 here if you
> > want the interrupt to fire at the correct time.
> 
> I double-checked and found that vdisplay is the value originally used by
> this driver, by the fbdev driver and by Xorg's mga driver.

Sure, but what does the hardware actually want?

-- 
Ville Syrjälä
Intel
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