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

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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@xxxxxxx>
> ---
>  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.

Sine linecomp also resets the memory address counter to 0 you
should probably see one bogus line at the bottom of the screen
if my recollection of that +1 is correct.

But maybe my memory is wrong.

> +
>  	WREG_GFX(0, 0);
>  	WREG_GFX(1, 0);
>  	WREG_GFX(2, 0);
> @@ -1063,12 +1071,12 @@ static int mga_crtc_mode_set(struct drm_crtc *crtc,
>  		 ((vdisplay & 0x100) >> 7) |
>  		 ((vsyncstart & 0x100) >> 6) |
>  		 ((vdisplay & 0x100) >> 5) |
> -		 ((vdisplay & 0x100) >> 4) | /* linecomp */
> +		 ((linecomp & 0x100) >> 4) |
>  		 ((vtotal & 0x200) >> 4)|
>  		 ((vdisplay & 0x200) >> 3) |
>  		 ((vsyncstart & 0x200) >> 2));
>  	WREG_CRT(9, ((vdisplay & 0x200) >> 4) |
> -		 ((vdisplay & 0x200) >> 3));
> +		 ((linecomp & 0x200) >> 3));
>  	WREG_CRT(10, 0);
>  	WREG_CRT(11, 0);
>  	WREG_CRT(12, 0);
> @@ -1083,7 +1091,7 @@ static int mga_crtc_mode_set(struct drm_crtc *crtc,
>  	WREG_CRT(21, vdisplay & 0xFF);
>  	WREG_CRT(22, (vtotal + 1) & 0xFF);
>  	WREG_CRT(23, 0xc3);
> -	WREG_CRT(24, vdisplay & 0xFF);
> +	WREG_CRT(24, linecomp & 0xff);
>  
>  	ext_vga[0] = 0;
>  	ext_vga[5] = 0;
> @@ -1099,7 +1107,7 @@ static int mga_crtc_mode_set(struct drm_crtc *crtc,
>  		((vdisplay & 0x400) >> 8) |
>  		((vdisplay & 0xc00) >> 7) |
>  		((vsyncstart & 0xc00) >> 5) |
> -		((vdisplay & 0x400) >> 3);
> +		((linecomp & 0x400) >> 3);
>  	if (fb->format->cpp[0] * 8 == 24)
>  		ext_vga[3] = (((1 << bppshift) * 3) - 1) | 0x80;
>  	else
> @@ -1411,6 +1419,30 @@ static void mga_crtc_disable(struct drm_crtc *crtc)
>  	crtc->primary->fb = NULL;
>  }
>  
> +static int mga_crtc_enable_vblank(struct drm_crtc *crtc)
> +{
> +	struct drm_device *dev = crtc->dev;
> +	struct mga_device *mdev = dev->dev_private;
> +	u32 ien;
> +
> +	ien = RREG32(0x1e1c);

MGAREG_IEN?

> +	ien |= 0x00000020; /* set <vlineien> */
> +	WREG32(0x1e1c, ien);
> +
> +	return 0;
> +}
> +
> +static void mga_crtc_disable_vblank(struct drm_crtc *crtc)
> +{
> +	struct drm_device *dev = crtc->dev;
> +	struct mga_device *mdev = dev->dev_private;
> +	u32 ien;
> +
> +	ien = RREG32(0x1e1c);
> +	ien &= 0xffffffdf; /* clear <vlineien> */
> +	WREG32(0x1e1c, ien);
> +}
> +
>  /* These provide the minimum set of functions required to handle a CRTC */
>  static const struct drm_crtc_funcs mga_crtc_funcs = {
>  	.cursor_set = mga_crtc_cursor_set,
> @@ -1418,6 +1450,8 @@ static const struct drm_crtc_funcs mga_crtc_funcs = {
>  	.gamma_set = mga_crtc_gamma_set,
>  	.set_config = drm_crtc_helper_set_config,
>  	.destroy = mga_crtc_destroy,
> +	.enable_vblank = mga_crtc_enable_vblank,
> +	.disable_vblank = mga_crtc_disable_vblank,
>  };
>  
>  static const struct drm_crtc_helper_funcs mga_helper_funcs = {
> -- 
> 2.23.0
> 
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> dri-devel@xxxxxxxxxxxxxxxxxxxxx
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Ville Syrjälä
Intel
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