Linux userland API discussions

* Re: [PATCH v2 2/3] fbcon: use the cursor blink interval provided by vt
From: Thierry Reding @ 2015-05-22 10:00 UTC (permalink / raw)
  To: Greg Kroah-Hartman
  Cc: Kevin Hilman, Scot Doyle, Tomi Valkeinen, Michael Kerrisk,
	Jiri Slaby, Jean-Christophe Plagniol-Villard, Pavel Machek,
	Geert Uytterhoeven, lkml, linux-fbdev, linux-man, linux-api,
	Tyler Baker, Olof Johansson, Daniel Stone, Arnd Bergmann
In-Reply-To: <20150522020031.GA3516@kroah.com>

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On Thu, May 21, 2015 at 07:00:31PM -0700, Greg Kroah-Hartman wrote:
> On Thu, May 21, 2015 at 10:00:50AM +0200, Thierry Reding wrote:
> > On Wed, May 20, 2015 at 09:26:38PM -0700, Greg Kroah-Hartman wrote:
> > > On Wed, May 20, 2015 at 02:36:17PM +0200, Thierry Reding wrote:
> > > > On Tue, May 19, 2015 at 04:41:12PM -0700, Greg Kroah-Hartman wrote:
> > > > > On Tue, May 19, 2015 at 11:52:29PM +0200, Thierry Reding wrote:
> > > > > > On Tue, May 19, 2015 at 02:45:19PM -0700, Kevin Hilman wrote:
> > > > > > > On Tue, May 19, 2015 at 2:40 PM, Thierry Reding
> > > > > > > <thierry.reding@gmail.com> wrote:
> > > > > > > > On Tue, May 19, 2015 at 02:15:41PM -0700, Kevin Hilman wrote:
> > > > > > > >> On Thu, Mar 26, 2015 at 6:56 AM, Scot Doyle <lkml14@scotdoyle.com> wrote:
> > > > > > > >> > vt now provides a cursor blink interval via vc_data. Use this
> > > > > > > >> > interval instead of the currently hardcoded 200 msecs. Store it in
> > > > > > > >> > fbcon_ops to avoid locking the console in cursor_timer_handler().
> > > > > > > >> >
> > > > > > > >> > Signed-off-by: Scot Doyle <lkml14@scotdoyle.com>
> > > > > > > >> > Acked-by: Pavel Machek <pavel@ucw.cz>
> > > > > > > >>
> > > > > > > >> This patch hit next-20150519 in the form of commit 27a4c827c34a
> > > > > > > >> (fbcon: use the cursor blink interval provided by vt) and has caused
> > > > > > > >> boot failure on a handful of ARM platforms when booting a MMC root
> > > > > > > >> filesystem.  This error was spotted by the kernelci.org bot on
> > > > > > > >> exynos5800-peach-pi[1] and Thierry and Daniel (Cc'd) have seen it on
> > > > > > > >> some tegra platforms too.
> > > > > > > >>
> > > > > > > >> Thierry spotted this commit as a potential cause, and both Daniel and
> > > > > > > >> I have reverted and boot tested on exynos5 and tegra respectively and
> > > > > > > >> the boot panics disappear.
> > > > > > > >
> > > > > > > > FWIW, if I apply the below on top of next-20150519 things seem to be
> > > > > > > > back to normal as well:
> > > > > > > >
> > > > > > > > diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
> > > > > > > > index 05b1d1a71ef9..658c34bb9076 100644
> > > > > > > > --- a/drivers/video/console/fbcon.c
> > > > > > > > +++ b/drivers/video/console/fbcon.c
> > > > > > > > @@ -1310,8 +1310,9 @@ static void fbcon_cursor(struct vc_data *vc, int mode)
> > > > > > > >                 return;
> > > > > > > >
> > > > > > > >         ops->cur_blink_jiffies = msecs_to_jiffies(vc->vc_cur_blink_ms);
> > > > > > > > -       fbcon_del_cursor_timer(info);
> > > > > > > > -       if (!(vc->vc_cursor_type & 0x10))
> > > > > > > > +       if (vc->vc_cursor_type & 0x10)
> > > > > > > > +               fbcon_del_cursor_timer(info);
> > > > > > > > +       else
> > > > > > > >                 fbcon_add_cursor_timer(info);
> > > > > > > >
> > > > > > > >         ops->cursor_flash = (mode == CM_ERASE) ? 0 : 1;
> > > > > > > 
> > > > > > > Applying this on next-20150519 makes my exynos board happily boot again as well.
> > > > > > > 
> > > > > > > Tested-by: Kevin Hilman <khilman@linaro.org>
> > > > > > 
> > > > > > Excellent. Greg, Scot, any opinions on whether or not this is the right
> > > > > > thing to do? It restores a bit that looks suspiciously like it snuck in
> > > > > > in the original (at least it isn't documented in the commit message).
> > > > > > 
> > > > > > Greg, feel free to squash this in if everybody agrees this is good to
> > > > > > go. If you prefer a patch on top let me know and I'll come up with a
> > > > > > proper commit message.
> > > > > 
> > > > > Please send a real patch and I'll apply it on top, as I can't rebase my
> > > > > public tree.
> > > > 
> > > > Attached.
> > > 
> > > Ugh, no, please resend it as a stand-alone patch, I can't easily apply
> > > attachments.
> > 
> > Really? Your MUA can't dissect multipart messages? Anyway, sent
> > separately for your convenience.
> 
> "git am" doesn't do that.  I apply patches in huge chunks of mbox files.

What I frequently end up doing is apply patches straight from mutt by
piping the mail or an attached patch to git am. I guess I had expected
that you'd have something similar to simplify applying patches.

> Remember, if I have to hand-edit, or do something special with your
> patch, I will not do it, you need to do it correctly to make
> maintainer's lives easier, not harder, given that maintainers are the
> limited resouce, not developers.

I understand. I'll make a mental note to never send you patches as
attachment again.

Thierry

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