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Date:   Tue, 5 Apr 2022 10:45:53 +0200
From:   Daniel Vetter <daniel@ffwll.ch>
To:     Thomas Zimmermann <tzimmermann@suse.de>
Cc:     Daniel Vetter <daniel.vetter@ffwll.ch>,
        DRI Development <dri-devel@lists.freedesktop.org>,
        linux-fbdev@vger.kernel.org, Du Cheng <ducheng2@gmail.com>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Claudio Suarez <cssk@net-c.es>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Daniel Vetter <daniel.vetter@intel.com>,
        Sam Ravnborg <sam@ravnborg.org>
Subject: Re: [PATCH v2 09/19] fbcon: Extract fbcon_open/release helpers
Message-ID: <YkwBwW6E9gbL2Sut@phenom.ffwll.local>
Mail-Followup-To: Thomas Zimmermann <tzimmermann@suse.de>,
        DRI Development <dri-devel@lists.freedesktop.org>,
        linux-fbdev@vger.kernel.org, Du Cheng <ducheng2@gmail.com>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
        LKML <linux-kernel@vger.kernel.org>, Claudio Suarez <cssk@net-c.es>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Daniel Vetter <daniel.vetter@intel.com>,
        Sam Ravnborg <sam@ravnborg.org>
References: <20220208210824.2238981-1-daniel.vetter@ffwll.ch>
 <20220208210824.2238981-10-daniel.vetter@ffwll.ch>
 <0879a2ff-37df-a9ae-0ce1-2bfcb2d1b322@suse.de>
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On Thu, Feb 10, 2022 at 12:46:32PM +0100, Thomas Zimmermann wrote:
> Hi
> 
> Am 08.02.22 um 22:08 schrieb Daniel Vetter:
> > There's two minor behaviour changes in here:
> > - in error paths we now consistently call fb_ops->fb_release
> > - fb_release really can't fail (fbmem.c ignores it too) and there's no
> >    reasonable cleanup we can do anyway.
> > 
> > Note that everything in fbcon.c is protected by the big console_lock()
> > lock (especially all the global variables), so the minor changes in
> > ordering of setup/cleanup do not matter.
> > 
> > v2: Explain a bit better why this is all correct (Sam)
> > 
> > Acked-by: Sam Ravnborg <sam@ravnborg.org>
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > Cc: Daniel Vetter <daniel@ffwll.ch>
> > Cc: Claudio Suarez <cssk@net-c.es>
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> > Cc: Du Cheng <ducheng2@gmail.com>
> > ---
> >   drivers/video/fbdev/core/fbcon.c | 107 +++++++++++++++----------------
> >   1 file changed, 53 insertions(+), 54 deletions(-)
> > 
> > diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> > index 058e885d24f6..3e1a3e7bf527 100644
> > --- a/drivers/video/fbdev/core/fbcon.c
> > +++ b/drivers/video/fbdev/core/fbcon.c
> > @@ -682,19 +682,37 @@ static int fbcon_invalid_charcount(struct fb_info *info, unsigned charcount)
> >   #endif /* CONFIG_MISC_TILEBLITTING */
> > +static int fbcon_open(struct fb_info *info)
> > +{
> > +	if (!try_module_get(info->fbops->owner))
> > +		return -ENODEV;
> > +
> > +	if (info->fbops->fb_open &&
> > +	    info->fbops->fb_open(info, 0)) {
> > +		module_put(info->fbops->owner);
> > +		return -ENODEV;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static void fbcon_release(struct fb_info *info)
> > +{
> > +	if (info->fbops->fb_release)
> > +		info->fbops->fb_release(info, 0);
> > +
> > +	module_put(info->fbops->owner);
> > +}
> >   static int con2fb_acquire_newinfo(struct vc_data *vc, struct fb_info *info,
> >   				  int unit, int oldidx)
> >   {
> >   	struct fbcon_ops *ops = NULL;
> > -	int err = 0;
> > -
> > -	if (!try_module_get(info->fbops->owner))
> > -		err = -ENODEV;
> > +	int err;
> > -	if (!err && info->fbops->fb_open &&
> > -	    info->fbops->fb_open(info, 0))
> > -		err = -ENODEV;
> > +	err = fbcon_open(info);
> > +	if (err)
> > +		return err;
> >   	if (!err) {
> >   		ops = kzalloc(sizeof(struct fbcon_ops), GFP_KERNEL);
> > @@ -715,7 +733,7 @@ static int con2fb_acquire_newinfo(struct vc_data *vc, struct fb_info *info,
> >   	if (err) {
> >   		con2fb_map[unit] = oldidx;
> > -		module_put(info->fbops->owner);
> > +		fbcon_release(info);
> >   	}
> >   	return err;
> > @@ -726,45 +744,34 @@ static int con2fb_release_oldinfo(struct vc_data *vc, struct fb_info *oldinfo,
> >   				  int oldidx, int found)
> >   {
> >   	struct fbcon_ops *ops = oldinfo->fbcon_par;
> > -	int err = 0, ret;
> > +	int ret;
> > -	if (oldinfo->fbops->fb_release &&
> > -	    oldinfo->fbops->fb_release(oldinfo, 0)) {
> > -		con2fb_map[unit] = oldidx;
> 
> We don't need oldidx any longer?
> 
> There's some logic wrt to the parameter 'found' here and in set_con2fb_map()
> that appears to be relevant.

Yeah further patches clean this up more. Or did you see a potential bug
here? I did ditch the fb_release error handling, simply because there's
not really much we can do anyway, it shouldn't ever fail (that's a driver
bug) and it was convoluting the code for no gain. But I might have missed
something in this cargo-cult.
-Daniel

> 
> Best regards
> Thomas
> 
> 
> > -		if (!found && newinfo->fbops->fb_release)
> > -			newinfo->fbops->fb_release(newinfo, 0);
> > -		if (!found)
> > -			module_put(newinfo->fbops->owner);
> > -		err = -ENODEV;
> > -	}
> > +	fbcon_release(oldinfo);
> > -	if (!err) {
> > -		fbcon_del_cursor_work(oldinfo);
> > -		kfree(ops->cursor_state.mask);
> > -		kfree(ops->cursor_data);
> > -		kfree(ops->cursor_src);
> > -		kfree(ops->fontbuffer);
> > -		kfree(oldinfo->fbcon_par);
> > -		oldinfo->fbcon_par = NULL;
> > -		module_put(oldinfo->fbops->owner);
> > -		/*
> > -		  If oldinfo and newinfo are driving the same hardware,
> > -		  the fb_release() method of oldinfo may attempt to
> > -		  restore the hardware state.  This will leave the
> > -		  newinfo in an undefined state. Thus, a call to
> > -		  fb_set_par() may be needed for the newinfo.
> > -		*/
> > -		if (newinfo && newinfo->fbops->fb_set_par) {
> > -			ret = newinfo->fbops->fb_set_par(newinfo);
> > +	fbcon_del_cursor_work(oldinfo);
> > +	kfree(ops->cursor_state.mask);
> > +	kfree(ops->cursor_data);
> > +	kfree(ops->cursor_src);
> > +	kfree(ops->fontbuffer);
> > +	kfree(oldinfo->fbcon_par);
> > +	oldinfo->fbcon_par = NULL;
> > +	/*
> > +	  If oldinfo and newinfo are driving the same hardware,
> > +	  the fb_release() method of oldinfo may attempt to
> > +	  restore the hardware state.  This will leave the
> > +	  newinfo in an undefined state. Thus, a call to
> > +	  fb_set_par() may be needed for the newinfo.
> > +	*/
> > +	if (newinfo && newinfo->fbops->fb_set_par) {
> > +		ret = newinfo->fbops->fb_set_par(newinfo);
> > -			if (ret)
> > -				printk(KERN_ERR "con2fb_release_oldinfo: "
> > -					"detected unhandled fb_set_par error, "
> > -					"error code %d\n", ret);
> > -		}
> > +		if (ret)
> > +			printk(KERN_ERR "con2fb_release_oldinfo: "
> > +				"detected unhandled fb_set_par error, "
> > +				"error code %d\n", ret);
> >   	}
> > -	return err;
> > +	return 0;
> >   }
> >   static void con2fb_init_display(struct vc_data *vc, struct fb_info *info,
> > @@ -919,7 +926,6 @@ static const char *fbcon_startup(void)
> >   	struct fbcon_display *p = &fb_display[fg_console];
> >   	struct vc_data *vc = vc_cons[fg_console].d;
> >   	const struct font_desc *font = NULL;
> > -	struct module *owner;
> >   	struct fb_info *info = NULL;
> >   	struct fbcon_ops *ops;
> >   	int rows, cols;
> > @@ -938,17 +944,12 @@ static const char *fbcon_startup(void)
> >   	if (!info)
> >   		return NULL;
> >   	
> > -	owner = info->fbops->owner;
> > -	if (!try_module_get(owner))
> > +	if (fbcon_open(info))
> >   		return NULL;
> > -	if (info->fbops->fb_open && info->fbops->fb_open(info, 0)) {
> > -		module_put(owner);
> > -		return NULL;
> > -	}
> >   	ops = kzalloc(sizeof(struct fbcon_ops), GFP_KERNEL);
> >   	if (!ops) {
> > -		module_put(owner);
> > +		fbcon_release(info);
> >   		return NULL;
> >   	}
> > @@ -3314,10 +3315,6 @@ static void fbcon_exit(void)
> >   		}
> >   		if (mapped) {
> > -			if (info->fbops->fb_release)
> > -				info->fbops->fb_release(info, 0);
> > -			module_put(info->fbops->owner);
> > -
> >   			if (info->fbcon_par) {
> >   				struct fbcon_ops *ops = info->fbcon_par;
> > @@ -3327,6 +3324,8 @@ static void fbcon_exit(void)
> >   				kfree(info->fbcon_par);
> >   				info->fbcon_par = NULL;
> >   			}
> > +
> > +			fbcon_release(info);
> >   		}
> >   	}
> >   }
> 
> -- 
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 N?rnberg, Germany
> (HRB 36809, AG N?rnberg)
> Gesch?ftsf?hrer: Ivo Totev


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