Re: [PATCH] drm/gud: rearrange gud_probe() to prepare for function splitting

[Ruben Wauters <rubenru09@aol.com>]

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On Mon, 2025-10-20 at 09:00 +0200, Thomas Zimmermann wrote:
> Hi
> 
> Am 19.10.25 um 20:53 schrieb Ruben Wauters:
> > gud_prove() is currently very large and does many things, including
> 
> 'gud_probe'

Unfortunate typo that I only realised after sending
> 
> > pipeline setup and feature detection, as well as having USB functions.
> > 
> > This patch re-orders the code in gud_probe() to make it more organised
> > and easier to split apart in the future.
> > 
> > Signed-off-by: Ruben Wauters <rubenru09@aol.com>
> > ---
> > I wanted to move mode config to just before pipeline init, however mode
> > config is edited in feature detection so I was unsure how to go about it
> > exactly.
> > Further untangling of this may be required before splitting it out
> > ---
> >   drivers/gpu/drm/gud/gud_drv.c | 31 +++++++++++++++++--------------
> >   1 file changed, 17 insertions(+), 14 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/gud/gud_drv.c b/drivers/gpu/drm/gud/gud_drv.c
> > index b7345c8d823d..583f7f8f4c00 100644
> > --- a/drivers/gpu/drm/gud/gud_drv.c
> > +++ b/drivers/gpu/drm/gud/gud_drv.c
> > @@ -463,10 +463,6 @@ static int gud_probe(struct usb_interface *intf, const struct usb_device_id *id)
> >   		return PTR_ERR(gdrm);
> >   
> >   	drm = &gdrm->drm;
> > -	drm->mode_config.funcs = &gud_mode_config_funcs;
> > -	ret = drmm_mode_config_init(drm);
> > -	if (ret)
> > -		return ret;
> >   
> >   	gdrm->flags = le32_to_cpu(desc.flags);
> >   	gdrm->compression = desc.compression & GUD_COMPRESSION_LZ4;
> > @@ -483,11 +479,18 @@ static int gud_probe(struct usb_interface *intf, const struct usb_device_id *id)
> >   	if (ret)
> >   		return ret;
> >   
> > +	/* Mode config init*/
> > +	ret = drmm_mode_config_init(drm);
> > +	if (ret)
> > +		return ret;
> > +
> >   	drm->mode_config.min_width = le32_to_cpu(desc.min_width);
> >   	drm->mode_config.max_width = le32_to_cpu(desc.max_width);
> >   	drm->mode_config.min_height = le32_to_cpu(desc.min_height);
> >   	drm->mode_config.max_height = le32_to_cpu(desc.max_height);
> > +	drm->mode_config.funcs = &gud_mode_config_funcs;
> >   
> > +	/*Format init*/
> >   	formats_dev = devm_kmalloc(dev, GUD_FORMATS_MAX_NUM, GFP_KERNEL);
> >   	/* Add room for emulated XRGB8888 */
> >   	formats = devm_kmalloc_array(dev, GUD_FORMATS_MAX_NUM + 1, sizeof(*formats), GFP_KERNEL);
> > @@ -587,6 +590,7 @@ static int gud_probe(struct usb_interface *intf, const struct usb_device_id *id)
> >   			return -ENOMEM;
> >   	}
> >   
> > +	/*Pipeline init*/
> >   	ret = drm_universal_plane_init(drm, &gdrm->plane, 0,
> >   				       &gud_plane_funcs,
> >   				       formats, num_formats,
> > @@ -598,15 +602,6 @@ static int gud_probe(struct usb_interface *intf, const struct usb_device_id *id)
> >   	drm_plane_helper_add(&gdrm->plane, &gud_plane_helper_funcs);
> >   	drm_plane_enable_fb_damage_clips(&gdrm->plane);
> >   
> > -	devm_kfree(dev, formats);
> > -	devm_kfree(dev, formats_dev);
> > -
> > -	ret = gud_get_properties(gdrm);
> > -	if (ret) {
> > -		dev_err(dev, "Failed to get properties (error=%d)\n", ret);
> > -		return ret;
> > -	}
> > -
> >   	ret = drm_crtc_init_with_planes(drm, &gdrm->crtc, &gdrm->plane, NULL,
> >   					&gud_crtc_funcs, NULL);
> >   	if (ret)
> > @@ -621,6 +616,13 @@ static int gud_probe(struct usb_interface *intf, const struct usb_device_id *id)
> >   	}
> >   
> >   	drm_mode_config_reset(drm);
> > +	drm_kms_helper_poll_init(drm);
> > +
> > +	ret = gud_get_properties(gdrm);
> 
> This function installs plane properties. So it need to be in its old 
> location after drm_universal_plane_init() and before 
> drm_mode_config_reset(). It should be renamed to 
> gud_plane_add_properties(). See [1] for the connector equivalent

This does make sense, though I do wonder why it worked on testing,
either way, will change it.
> 
> [1] 
> https://elixir.bootlin.com/linux/v6.18-rc1/source/drivers/gpu/drm/gud/gud_connector.c#L474
> 
> > +	if (ret) {
> > +		dev_err(dev, "Failed to get properties (error=%d)\n", ret);
> > +		return ret;
> > +	}
> >   
> 
> >   	usb_set_intfdata(intf, gdrm);
> 
> After you've called drm_kms_helper_poll_init(), DRM could query the 
> connector for attached displays at any time. This might require the usb 
> interface to point to the gud device. And the DRM driver also needs to 
> know about the DMA device.  I quick look through the driver code suggest 
> that it works without, but better not count on it.
> 
> Best would be to move this line and the block with the DMA setup [2] 
> just after where the gud device got allocated with devmdrm_dev_alloc(). [3]
> 
> [2] 
> https://elixir.bootlin.com/linux/v6.18-rc1/source/drivers/gpu/drm/gud/gud_drv.c#L627
> [3] 
> https://elixir.bootlin.com/linux/v6.18-rc1/source/drivers/gpu/drm/gud/gud_drv.c#L464

Will do, I'll send a v2 patch with the requested changes.
> 
> Best regards
> Thomas
> 
> >   
> > @@ -638,7 +640,8 @@ static int gud_probe(struct usb_interface *intf, const struct usb_device_id *id)
> >   	if (ret)
> >   		return ret;
> >   
> > -	drm_kms_helper_poll_init(drm);
> > +	devm_kfree(dev, formats);
> > +	devm_kfree(dev, formats_dev);
> >   
> >   	drm_client_setup(drm, NULL);
> >   

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