Subject: Re: [PATCH v3 05/16] drm/fb-helper: do a generic fb_setcmap helper in
 terms of crtc .gamma_set
To: linux-kernel@vger.kernel.org,
        Boris Brezillon <boris.brezillon@free-electrons.com>,
        dri-devel@lists.freedesktop.org,
        Daniel Vetter <daniel.vetter@intel.com>
References: <1499164632-5582-1-git-send-email-peda@axentia.se>
 <1499164632-5582-6-git-send-email-peda@axentia.se>
 <20170705062144.bdyngsas4uc5dj2d@phenom.ffwll.local>
From: Peter Rosin <peda@axentia.se>
Organization: Axentia Technologies AB
Message-ID: <3cbc02dc-e535-7d66-923b-c9a4d0f14f13@axentia.se>
Date: Wed, 5 Jul 2017 19:50:49 +0200
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On 2017-07-05 08:21, Daniel Vetter wrote:
> On Tue, Jul 04, 2017 at 12:37:01PM +0200, Peter Rosin wrote:
>> This makes the redundant fb helpers .load_lut, .gamma_set and .gamma_get
>> completely obsolete.
>>
>> Signed-off-by: Peter Rosin <peda@axentia.se>
>> ---
>>  drivers/gpu/drm/drm_fb_helper.c | 165 +++++++++++++++++++++++-----------------
>>  1 file changed, 94 insertions(+), 71 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
>> index b75b1f2..7f8199a 100644
>> --- a/drivers/gpu/drm/drm_fb_helper.c
>> +++ b/drivers/gpu/drm/drm_fb_helper.c
>> @@ -1257,27 +1257,6 @@ void drm_fb_helper_set_suspend_unlocked(struct drm_fb_helper *fb_helper,
>>  }
>>  EXPORT_SYMBOL(drm_fb_helper_set_suspend_unlocked);
>>  
>> -static int setcolreg(struct drm_crtc *crtc, u16 red, u16 green,
>> -		     u16 blue, u16 regno, struct fb_info *info)
>> -{
>> -	struct drm_fb_helper *fb_helper = info->par;
>> -	struct drm_framebuffer *fb = fb_helper->fb;
>> -
>> -	/*
>> -	 * The driver really shouldn't advertise pseudo/directcolor
>> -	 * visuals if it can't deal with the palette.
>> -	 */
>> -	if (WARN_ON(!fb_helper->funcs->gamma_set ||
>> -		    !fb_helper->funcs->gamma_get))
>> -		return -EINVAL;
>> -
>> -	WARN_ON(fb->format->cpp[0] != 1);
>> -
>> -	fb_helper->funcs->gamma_set(crtc, red, green, blue, regno);
>> -
>> -	return 0;
>> -}
>> -
>>  static int setcmap_pseudo_palette(struct fb_cmap *cmap, struct fb_info *info)
>>  {
>>  	u32 *palette = (u32 *)info->pseudo_palette;
>> @@ -1310,54 +1289,68 @@ static int setcmap_pseudo_palette(struct fb_cmap *cmap, struct fb_info *info)
>>  	return 0;
>>  }
>>  
>> -/**
>> - * drm_fb_helper_setcmap - implementation for &fb_ops.fb_setcmap
>> - * @cmap: cmap to set
>> - * @info: fbdev registered by the helper
>> - */
>> -int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
>> +static int setcmap_legacy(struct fb_cmap *cmap, struct fb_info *info)
>>  {
>>  	struct drm_fb_helper *fb_helper = info->par;
>> -	struct drm_device *dev = fb_helper->dev;
>> -	const struct drm_crtc_helper_funcs *crtc_funcs;
>> -	u16 *red, *green, *blue, *transp;
>>  	struct drm_crtc *crtc;
>>  	u16 *r, *g, *b;
>> -	int i, j, rc = 0;
>> -	int start;
>> +	int i, ret = 0;
>>  
>> -	if (oops_in_progress)
>> -		return -EBUSY;
>> +	for (i = 0; i < fb_helper->crtc_count; i++) {
>> +		crtc = fb_helper->crtc_info[i].mode_set.crtc;
>> +		if (!crtc->funcs->gamma_set || !crtc->gamma_size)
>> +			return -EINVAL;
>>  
>> -	mutex_lock(&fb_helper->lock);
>> -	if (!drm_fb_helper_is_bound(fb_helper)) {
>> -		mutex_unlock(&fb_helper->lock);
>> -		return -EBUSY;
>> -	}
>> +		if (cmap->start + cmap->len > crtc->gamma_size)
>> +			return -EINVAL;
>>  
>> -	drm_modeset_lock_all(dev);
>> -	if (info->fix.visual == FB_VISUAL_TRUECOLOR) {
>> -		rc = setcmap_pseudo_palette(cmap, info);
>> -		goto out;
>> +		r = crtc->gamma_store;
>> +		g = r + crtc->gamma_size;
>> +		b = g + crtc->gamma_size;
>> +
>> +		memcpy(r + cmap->start, cmap->red, cmap->len * sizeof(*r));
>> +		memcpy(g + cmap->start, cmap->green, cmap->len * sizeof(*g));
>> +		memcpy(b + cmap->start, cmap->blue, cmap->len * sizeof(*b));
>> +
>> +		ret = crtc->funcs->gamma_set(crtc, r, g, b,
>> +					     crtc->gamma_size, NULL);
>> +		if (ret)
>> +			return ret;
>>  	}
>>  
>> -	for (i = 0; i < fb_helper->crtc_count; i++) {
>> -		crtc = fb_helper->crtc_info[i].mode_set.crtc;
>> -		crtc_funcs = crtc->helper_private;
>> +	return ret;
>> +}
> 
> For the legacy path you need to keep the drm_modeset_lock_all (but only in
> setcmap_legacy). Otherwise this part here looks good.

Oops, didn't intend to zap that one. Thanks for catching!

>>  
>> -		red = cmap->red;
>> -		green = cmap->green;
>> -		blue = cmap->blue;
>> -		transp = cmap->transp;
>> -		start = cmap->start;
>> +static int setcmap_atomic(struct fb_cmap *cmap, struct fb_info *info)
>> +{
>> +	struct drm_fb_helper *fb_helper = info->par;
>> +	struct drm_device *dev = fb_helper->dev;
>> +	struct drm_modeset_acquire_ctx ctx;
>> +	struct drm_crtc_state *crtc_state;
>> +	struct drm_atomic_state *state;
>> +	struct drm_crtc *crtc;
>> +	u16 *r, *g, *b;
>> +	int i, ret = 0;
>>  
>> -		if (!crtc->gamma_size) {
>> -			rc = -EINVAL;
>> +	state = drm_atomic_state_alloc(dev);
>> +	if (!state)
>> +		return -ENOMEM;
>> +	drm_modeset_acquire_init(&ctx, 0);
>> +retry:
>> +	ret = drm_modeset_lock_all_ctx(dev, &ctx);
> 
> With atomic you don't need to grab locks, this is done behind the scenes
> (as long as you handle the retry/backoff correctly). See the kerneldoc for
> the various drm_atomic_get_*_state functions.

It doesn't work if I remove it. What is the disconnect?

>> +	if (ret)
>> +		goto fini;
>> +	state->acquire_ctx = &ctx;
>> +	for (i = 0; i < fb_helper->crtc_count; i++) {
>> +		crtc = fb_helper->crtc_info[i].mode_set.crtc;
>> +		if (!crtc->funcs->gamma_set) {
>> +			ret = -EINVAL;
>>  			goto out;
>>  		}
>>  
>> -		if (cmap->start + cmap->len > crtc->gamma_size) {
>> -			rc = -EINVAL;
>> +		crtc_state = drm_atomic_get_crtc_state(state, crtc);
>> +		if (IS_ERR(crtc_state)) {
>> +			ret = PTR_ERR(crtc_state);
>>  			goto out;
>>  		}
>>  
>> @@ -1369,27 +1362,57 @@ int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
>>  		memcpy(g + cmap->start, cmap->green, cmap->len * sizeof(*g));
>>  		memcpy(b + cmap->start, cmap->blue, cmap->len * sizeof(*b));
>>  
>> -		for (j = 0; j < cmap->len; j++) {
>> -			u16 hred, hgreen, hblue, htransp = 0xffff;
>> +		ret = crtc->funcs->gamma_set(crtc, r, g, b,
>> +					     crtc->gamma_size, crtc_state);
> 
> I guess my description of what I have in mind wasn't really clear. I think
> a proper atomic commit should never reuse one of the old hooks
> (->gamma_set) here, that's just confusing. Instead what I had in mind is
> to do the proper adjusting that gamma_set does here in this function, i.e.
> 
> - create the new blob, fill it with the cmap data
> 
> - assign that blob to the crtc state:
> 
> 	drm_atomic_replace_property_blob(&crtc_state->gamma_lut,
> 					 new_table, &temp);

That function is static, and...

>   Note that the drm_atomic_helper_legacy_gamma_set() does that in the most
>   convoluted way by going through a few layers.
> 
> - The one thing you need to do on top is check that the gamma_lut property
>   is supported (just check whether dev->mode_config.gamma_lut_property
>   exists). That check is instead of checking for ->gamma_set.

...drm_atomic_helper_legacy_gamma_set calls drm_atomic_crtc_set_property
which is already exported and performs all the checks I can think of...

> Checking for matching size is optional, the driver must do that already
> (for the atomic property).

...except this one.

> This way your previous patch isn't needed, and we don't need to change all
> the legacy callbacks. The only downside is that we duplicate a bit of the
> atomic commit setup scaffolding, but that's imo ok. You could extract that
> into a helper function shared between this code here and
> drm_atomic_helper_legacy_gamma_set(), but that seems frankly overkill to
> me. Creating atomic commits in the kernel is simply a bit verbose, but the
> benefit of the current framework is that the driver side looks a lot
> simpler.

But, yup, ditching 4/16 feels very nice. I'll mimic the code in
drm_atomic_helper_legacy_gamma_set for the v4 version of setcmap_atomic.

Good suggestion, and thanks for the more verbose explanation.

>> +		if (ret)
>> +			goto out;
>> +	}
>>  
>> -			hred = *red++;
>> -			hgreen = *green++;
>> -			hblue = *blue++;
>> +	ret = drm_atomic_commit(state);
>> +	if (ret == -EDEADLK) {
>> +		drm_modeset_backoff(&ctx);
>> +		goto retry;
>> +	}
>>  
>> -			if (transp)
>> -				htransp = *transp++;
>> +out:
>> +	drm_modeset_drop_locks(&ctx);
>> +fini:
>> +	drm_modeset_acquire_fini(&ctx);
>> +	drm_atomic_state_put(state);
>>  
>> -			rc = setcolreg(crtc, hred, hgreen, hblue, start++, info);
>> -			if (rc)
>> -				goto out;
>> -		}
>> -		if (crtc_funcs->load_lut)
>> -			crtc_funcs->load_lut(crtc);
>> +	return ret;
>> +}
>> +
>> +/**
>> + * drm_fb_helper_setcmap - implementation for &fb_ops.fb_setcmap
>> + * @cmap: cmap to set
>> + * @info: fbdev registered by the helper
>> + */
>> +int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
>> +{
>> +	struct drm_fb_helper *fb_helper = info->par;
>> +	int ret;
>> +
>> +	if (oops_in_progress)
>> +		return -EBUSY;
>> +
>> +	mutex_lock(&fb_helper->lock);
>> +
>> +	if (!drm_fb_helper_is_bound(fb_helper)) {
>> +		mutex_unlock(&fb_helper->lock);
>> +		return -EBUSY;
>>  	}
>> - out:
>> -	drm_modeset_unlock_all(dev);
>> +
>> +	if (info->fix.visual == FB_VISUAL_TRUECOLOR)
>> +		ret = setcmap_pseudo_palette(cmap, info);
>> +	else if (drm_drv_uses_atomic_modeset(fb_helper->dev))
>> +		ret = setcmap_atomic(cmap, info);
>> +	else
>> +		ret = setcmap_legacy(cmap, info);
>> +
>>  	mutex_unlock(&fb_helper->lock);
>> -	return rc;
>> +
>> +	return ret;
>>  }
>>  EXPORT_SYMBOL(drm_fb_helper_setcmap);
> 
> Besides the 2 comments this looks good and will get my r-b once revised.
> 
> Also on patches 1-3:
> 
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Excellent!

Cheers,
peda

> Cheers, Daniel
>>  
>> -- 
>> 2.1.4
>>
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>