linux-kernel - Re: [PATCH v3 0/5] console: Miscellaneous clean-ups, do not use FNTCHARCNT() in fbcon.c

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Message-ID: <20201114081021.GA11811@PWN>
Date:   Sat, 14 Nov 2020 03:10:21 -0500
From:   Peilin Ye <yepeilin.cs@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     Jiri Slaby <jirislaby@...nel.org>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org
Subject: Re: [PATCH v3 0/5] console: Miscellaneous clean-ups, do not use
 FNTCHARCNT() in fbcon.c

> On Fri, Nov 13, 2020 at 10:16:33PM +0100, Daniel Vetter wrote:
> > On Thu, Nov 12, 2020 at 07:02:21AM -0500, Peilin Ye wrote:
> > > Peilin Ye (5):
> > >   console: Delete unused con_font_copy() callback implementations
> > >   console: Delete dummy con_font_set() and con_font_default() callback implementations
> > >   Fonts: Add charcount field to font_desc
> > >   parisc/sticore: Avoid hard-coding built-in font charcount
> > >   fbcon: Avoid using FNTCHARCNT() and hard-coded built-in font charcount
> > 
> > Patches all look good to me, if Greg is ok with me applying the entire
> > pile to drm-misc-next I'll do that next week.

On Fri, Nov 13, 2020 at 11:47:51PM +0100, Greg Kroah-Hartman wrote:
> Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

Thanks for reviewing!  Questions about the last patch [5/5] though, it
depends on the following assumption:

"""
For each console `idx`, `vc_cons[idx].d->vc_font.data` and
`fb_display[idx].fontdata` always point to the same buffer.
"""

Is this true?  I think it is true by grepping for `fontdata`.  I also
noticed that fbcon.c is using `vc->vc_font.data` and `p->fontdata`
interchangeably, see fbcon_get_requirement():

		vc = vc_cons[fg_console].d;
		[...]
			p = &fb_display[fg_console];
			caps->x = 1 << (vc->vc_font.width - 1);
					^^^^^^^^^^^
			caps->y = 1 << (vc->vc_font.height - 1);
					^^^^^^^^^^^
			caps->len = (p->userfont) ?
				FNTCHARCNT(p->fontdata) : 256;
					   ^^^^^^^^^^^

If it is true, then what is the point of using `fontdata` in `struct
fbcon_display`?  Just for the `userfont` flag?  Should we delete
`fontdata`, when we no longer need the `userfont` flag?

In this sense I think [5/5] needs more testing.  Do we have test files
for fbcon, or should I try to write some tests from scratch?

Thank you,
Peilin Ye