Re: [PATCH 2/6] drm: Add drm_simple_encoder_{init,create}()

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Feb 07, 2020 at 03:36:49PM +0100, Noralf Trønnes wrote:
> 
> 
> Den 07.02.2020 09.41, skrev Thomas Zimmermann:
> > The simple-encoder helpers initialize an encoder with an empty
> > implementation. This covers the requirements of most of the existing
> > DRM drivers. A call to drm_simple_encoder_create() allocates and
> > initializes an encoder instance, a call to drm_simple_encoder_init()
> > initializes a pre-allocated instance.
> > 
> > Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> > ---
> >  drivers/gpu/drm/drm_encoder.c | 116 ++++++++++++++++++++++++++++++++++
> >  include/drm/drm_encoder.h     |  10 +++
> >  2 files changed, 126 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/drm_encoder.c b/drivers/gpu/drm/drm_encoder.c
> 
> <snip>
> 
> > +/**
> > + * drm_simple_encoder_create - Allocate and initialize an encoder
> > + * @dev: drm device
> > + * @encoder_type: user visible type of the encoder
> > + * @name: printf style format string for the encoder name, or NULL for
> > + *        default name
> > + *
> > + * Allocates and initialises an encoder that has no further functionality. The
> > + * encoder will be released automatically.
> > + *
> > + * Returns:
> > + * The encoder on success, a pointer-encoder error code on failure.
> > + */
> > +struct drm_encoder *drm_simple_encoder_create(struct drm_device *dev,
> > +					      int encoder_type,
> > +					      const char *name, ...)
> > +{
> > +	char *namestr = NULL;
> > +	struct drm_encoder *encoder;
> > +	int ret;
> > +
> > +	encoder = devm_kzalloc(dev->dev, sizeof(*encoder), GFP_KERNEL);
> 
> The encoder can outlive the devres if the device is unbound when
> userspace has open fds, so you can't use devm_ here.

Ah yes great catch. Rule of thumb: Never use devm_ for any drm_*
structure. It's wrong.

There's a todo somewhere to essentially create a drm_managed set of apis
where the cleanup matches the right lifetime - we need to only
free/release drm resource at drm_driver->release time.
-Daniel

> 
> Noralf.
> 
> > +	if (!encoder)
> > +		return ERR_PTR(-ENOMEM);
> > +
> > +	if (name) {
> > +		va_list ap;
> > +
> > +		va_start(ap, name);
> > +		namestr = kvasprintf(GFP_KERNEL, name, ap);
> > +		va_end(ap);
> > +		if (!namestr) {
> > +			ret = -ENOMEM;
> > +			goto err_devm_kfree;
> > +		}
> > +	}
> > +
> > +	ret = __drm_encoder_init(dev, encoder,
> > +				 &drm_simple_encoder_funcs_destroy,
> > +				 encoder_type, namestr);
> > +	if (ret)
> > +		goto err_kfree;
> > +
> > +	return encoder;
> > +
> > +err_kfree:
> > +	if (name)
> > +		kfree(namestr);
> > +err_devm_kfree:
> > +	devm_kfree(dev->dev, encoder);
> > +	return ERR_PTR(ret);
> > +}
> > +EXPORT_SYMBOL(drm_simple_encoder_create);
> > +

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch