Re: [PATCH v2 1/2] console: Remove dummy con_font_op() callback implementations

From: Daniel Vetter <daniel@ffwll.ch>
To: Jiri Slaby <jirislaby@kernel.org>
Cc: Peilin Ye <yepeilin.cs@gmail.com>,
	Daniel Vetter <daniel.vetter@ffwll.ch>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Thomas Winischhofer <thomas@winischhofer.net>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	Nicolas Pitre <nico@fluxnic.net>,
	"Gustavo A . R . Silva" <gustavoars@kernel.org>,
	Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
	George Kennedy <george.kennedy@oracle.com>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Peter Rosin <peda@axentia.se>,
	linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org,
	dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org
Subject: Re: [PATCH v2 1/2] console: Remove dummy con_font_op() callback implementations
Date: Mon, 2 Nov 2020 11:13:47 +0100	[thread overview]
Message-ID: <20201102101347.GN401619@phenom.ffwll.local> (raw)
In-Reply-To: <a8157089-bc72-c409-c7cc-2fd7eb087ebc@kernel.org>

On Mon, Nov 02, 2020 at 10:47:55AM +0100, Jiri Slaby wrote:
> On 02. 11. 20, 10:36, Peilin Ye wrote:
> > `struct console_font` is a UAPI structure, thus ideally should not be
> > used for kernel internal abstraction. Remove some dummy .con_font_set,
> > .con_font_default and .con_font_copy `struct consw` callback
> > implementations, to make it cleaner.
> 
> ESEMANTIC_ERROR.
> 
> 1) What do you refer to with the last "it"?
> 
> 2) What's the purpose of mentioning struct console_font at all?
> 
> 3) Could you clarify whether you checked it is safe to remove the hooks?
> 
> 4) All the hooks now return ENOSYS for both consoles (and not 0). Is this
> intentional?
> 
> I know answers to the first 3 questions, but you need to elaborate a bit in
> the commit log to connect those sentences. Esp. for people not dealing with
> the code on a daily basis. Ad 4) I am not sure.

Yup the behaviour change from 4) needs to be called out. I think this
should then also be done as part of the large patch series to remove the
dummy functions from all console drivers.

I don't expect the errno change to cause trouble, and it's the more honest
errno - changing fonts not supported is the truth. But if it is, we can
patch that up appropriately when we get a regression report. That's kinda
unavoidable with old crufty uapi like this one here.

Also a bikeshed: Additional information like the patch changelog or
reasons why you do something is imo best to include in the commit message
itself. It ends up looking a bit less tidy sometimes, but often there's
crucial information in these parts that was accidentally left out from the
commit message.
Thanks, Daniel
> 
> > Suggested-by: Daniel Vetter <daniel@ffwll.ch>
> > Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
> > ---
> > Change in v2:
> >    - [v2 2/2] no longer Cc: stable, so do not Cc: stable
> > 
> > Context: https://lore.kernel.org/lkml/CAKMK7uFY2zv0adjKJ_ORVFT7Zzwn075MaU0rEU7_FuqENLR=UA@mail.gmail.com/
> > 
> >   drivers/usb/misc/sisusbvga/sisusb_con.c | 21 ---------------------
> >   drivers/video/console/dummycon.c        | 20 --------------------
> >   2 files changed, 41 deletions(-)
> > 
> > diff --git a/drivers/usb/misc/sisusbvga/sisusb_con.c b/drivers/usb/misc/sisusbvga/sisusb_con.c
> > index c63e545fb105..dfa0d5ce6012 100644
> > --- a/drivers/usb/misc/sisusbvga/sisusb_con.c
> > +++ b/drivers/usb/misc/sisusbvga/sisusb_con.c
> > @@ -1345,24 +1345,6 @@ static int sisusbdummycon_blank(struct vc_data *vc, int blank, int mode_switch)
> >   	return 0;
> >   }
> > -static int sisusbdummycon_font_set(struct vc_data *vc,
> > -				   struct console_font *font,
> > -				   unsigned int flags)
> > -{
> > -	return 0;
> > -}
> > -
> > -static int sisusbdummycon_font_default(struct vc_data *vc,
> > -				       struct console_font *font, char *name)
> > -{
> > -	return 0;
> > -}
> > -
> > -static int sisusbdummycon_font_copy(struct vc_data *vc, int con)
> > -{
> > -	return 0;
> > -}
> > -
> >   static const struct consw sisusb_dummy_con = {
> >   	.owner =		THIS_MODULE,
> >   	.con_startup =		sisusbdummycon_startup,
> > @@ -1375,9 +1357,6 @@ static const struct consw sisusb_dummy_con = {
> >   	.con_scroll =		sisusbdummycon_scroll,
> >   	.con_switch =		sisusbdummycon_switch,
> >   	.con_blank =		sisusbdummycon_blank,
> > -	.con_font_set =		sisusbdummycon_font_set,
> > -	.con_font_default =	sisusbdummycon_font_default,
> > -	.con_font_copy =	sisusbdummycon_font_copy,
> >   };
> >   int
> > diff --git a/drivers/video/console/dummycon.c b/drivers/video/console/dummycon.c
> > index 2a0d0bda7faa..f1711b2f9ff0 100644
> > --- a/drivers/video/console/dummycon.c
> > +++ b/drivers/video/console/dummycon.c
> > @@ -124,23 +124,6 @@ static int dummycon_switch(struct vc_data *vc)
> >   	return 0;
> >   }
> > -static int dummycon_font_set(struct vc_data *vc, struct console_font *font,
> > -			     unsigned int flags)
> > -{
> > -	return 0;
> > -}
> > -
> > -static int dummycon_font_default(struct vc_data *vc,
> > -				 struct console_font *font, char *name)
> > -{
> > -	return 0;
> > -}
> > -
> > -static int dummycon_font_copy(struct vc_data *vc, int con)
> > -{
> > -	return 0;
> > -}
> > -
> >   /*
> >    *  The console `switch' structure for the dummy console
> >    *
> > @@ -159,8 +142,5 @@ const struct consw dummy_con = {
> >   	.con_scroll =	dummycon_scroll,
> >   	.con_switch =	dummycon_switch,
> >   	.con_blank =	dummycon_blank,
> > -	.con_font_set =	dummycon_font_set,
> > -	.con_font_default =	dummycon_font_default,
> > -	.con_font_copy =	dummycon_font_copy,
> >   };
> >   EXPORT_SYMBOL_GPL(dummy_con);
> > 
> 
> 
> -- 
> js
> suse labs

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