From: Javier Martinez Canillas <javierm@redhat.com>
To: Thomas Zimmermann <tzimmermann@suse.de>,
daniel@ffwll.ch, sam@ravnborg.org, deller@gmx.de,
geert+renesas@glider.be, lee@kernel.org,
daniel.thompson@linaro.org, jingoohan1@gmail.com
Cc: Steve Glendinning <steve.glendinning@shawell.net>,
linux-fbdev@vger.kernel.org, linux-sh@vger.kernel.org,
linux-staging@lists.linux.dev, dri-devel@lists.freedesktop.org,
linux-omap@vger.kernel.org
Subject: Re: [PATCH 22/30] fbdev/smscufx: Detect registered fb_info from refcount
Date: Mon, 12 Jun 2023 12:40:20 +0200 [thread overview]
Message-ID: <87mt152cbv.fsf@minerva.mail-host-address-is-not-set> (raw)
In-Reply-To: <7f62aa10-bc6f-96e2-d2cc-d42f0fad9e32@suse.de>
Thomas Zimmermann <tzimmermann@suse.de> writes:
Hello Thomas,
> Hi Javier
>
> Am 08.06.23 um 00:22 schrieb Javier Martinez Canillas:
>> Thomas Zimmermann <tzimmermann@suse.de> writes:
>>
>>> Detect registered instances of fb_info by reading the reference
>>> counter from struct fb_info.read. Avoids looking at the dev field
>>> and prepares fbdev for making struct fb_info.dev optional.
>>>
>>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
>>> Cc: Steve Glendinning <steve.glendinning@shawell.net>
>>> ---
>>> drivers/video/fbdev/smscufx.c | 4 ++--
>>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/video/fbdev/smscufx.c b/drivers/video/fbdev/smscufx.c
>>> index 17cec62cc65d..adb2b1fe8383 100644
>>> --- a/drivers/video/fbdev/smscufx.c
>>> +++ b/drivers/video/fbdev/smscufx.c
>>> @@ -1496,7 +1496,7 @@ static int ufx_setup_modes(struct ufx_data *dev, struct fb_info *info,
>>> u8 *edid;
>>> int i, result = 0, tries = 3;
>>>
>>> - if (info->dev) /* only use mutex if info has been registered */
>>> + if (refcount_read(&info->count)) /* only use mutex if info has been registered */
>>
>> The struct fb_info .count refcount is protected by the registration_lock
>> mutex in register_framebuffer(). I think this operation isn't thread safe ?
>
> It's an atomic read.
>
> https://elixir.bootlin.com/linux/latest/source/include/linux/refcount.h#L147
>
Yes, is an atomic read but by reading [0] my understanding is that does
not provide memory ordering guarantees. Maybe I misunderstood though...
[0]: https://www.kernel.org/doc/html/latest/core-api/refcount-vs-atomic.html
> And that function is only being called from the USB probe callback
> before registering the framebuffer. It's not clear to me how the value
> could be anything but zero. I'd best leave it as is with the ref counter.
>
Yes, I'm OK with that and as mentioned I don't think that's less safe
than the previous info->dev check with regard to race conditions.
--
Best regards,
Javier Martinez Canillas
Core Platforms
Red Hat
next prev parent reply other threads:[~2023-06-12 10:40 UTC|newest]
Thread overview: 190+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-05 14:47 [PATCH 00/30] fbdev: Make userspace interfaces optional Thomas Zimmermann
2023-06-05 14:47 ` Thomas Zimmermann
2023-06-05 14:47 ` [PATCH 01/30] backlight/bd6107: Compare against struct fb_info.device Thomas Zimmermann
2023-06-05 14:47 ` Thomas Zimmermann
2023-06-07 7:30 ` Javier Martinez Canillas
2023-06-07 7:30 ` Javier Martinez Canillas
2023-06-07 7:34 ` Javier Martinez Canillas
2023-06-07 7:34 ` Javier Martinez Canillas
2023-06-05 14:47 ` [PATCH 02/30] backlight/gpio_backlight: " Thomas Zimmermann
2023-06-05 14:47 ` Thomas Zimmermann
2023-06-05 20:19 ` Ruhl, Michael J
2023-06-05 20:23 ` Sam Ravnborg
2023-06-05 20:23 ` Sam Ravnborg
2023-06-05 20:41 ` Ruhl, Michael J
2023-06-05 20:41 ` Ruhl, Michael J
2023-06-06 7:24 ` Thomas Zimmermann
2023-06-06 7:49 ` Dan Carpenter
2023-06-06 7:49 ` Dan Carpenter
2023-06-06 8:05 ` Thomas Zimmermann
2023-06-06 8:05 ` Thomas Zimmermann
2023-06-05 14:47 ` [PATCH 03/30] backlight/lv5207lp: " Thomas Zimmermann
2023-06-05 14:47 ` Thomas Zimmermann
2023-06-07 7:35 ` Javier Martinez Canillas
2023-06-05 14:47 ` [PATCH 04/30] fbdev/atyfb: Reorder backlight and framebuffer init/cleanup Thomas Zimmermann
2023-06-05 14:47 ` Thomas Zimmermann
2023-06-07 7:36 ` Javier Martinez Canillas
2023-06-07 7:36 ` Javier Martinez Canillas
2023-06-05 14:47 ` [PATCH 05/30] fbdev/atyfb: Use hardware device as backlight parent Thomas Zimmermann
2023-06-05 14:47 ` Thomas Zimmermann
2023-06-07 7:41 ` Javier Martinez Canillas
2023-06-07 7:41 ` Javier Martinez Canillas
2023-06-05 14:47 ` [PATCH 06/30] fbdev/aty128fb: Reorder backlight and framebuffer init/cleanup Thomas Zimmermann
2023-06-05 14:47 ` Thomas Zimmermann
2023-06-07 7:42 ` Javier Martinez Canillas
2023-06-07 7:42 ` Javier Martinez Canillas
2023-06-05 14:47 ` [PATCH 07/30] fbdev/aty128fb: Use hardware device as backlight parent Thomas Zimmermann
2023-06-05 14:47 ` Thomas Zimmermann
2023-06-07 7:55 ` Javier Martinez Canillas
2023-06-07 7:55 ` Javier Martinez Canillas
2023-06-05 14:47 ` [PATCH 08/30] fbdev/broadsheetfb: Call device_remove_file() with hardware device Thomas Zimmermann
2023-06-05 14:47 ` Thomas Zimmermann
2023-06-07 7:55 ` Javier Martinez Canillas
2023-06-05 14:47 ` [PATCH 09/30] fbdev/ep93xx-fb: Alloc DMA memory from " Thomas Zimmermann
2023-06-05 14:47 ` Thomas Zimmermann
2023-06-07 8:47 ` Javier Martinez Canillas
2023-06-07 8:47 ` Javier Martinez Canillas
2023-06-05 14:47 ` [PATCH 10/30] fbdev/ep93xx-fb: Output messages with fb_info() and fb_err() Thomas Zimmermann
2023-06-05 14:47 ` Thomas Zimmermann
2023-06-07 8:59 ` Javier Martinez Canillas
2023-06-07 8:59 ` Javier Martinez Canillas
2023-06-05 14:47 ` [PATCH 11/30] fbdev/ep93xx-fb: Do not assign to struct fb_info.dev Thomas Zimmermann
2023-06-05 14:47 ` Thomas Zimmermann
2023-06-06 5:26 ` Dan Carpenter
2023-06-06 5:26 ` Dan Carpenter
2023-06-07 9:00 ` Javier Martinez Canillas
2023-06-07 9:00 ` Javier Martinez Canillas
2023-06-05 14:47 ` [PATCH 12/30] fbdev/mb862xxfb: Output messages with fb_dbg() and fb_err() Thomas Zimmermann
2023-06-05 14:47 ` Thomas Zimmermann
2023-06-07 9:00 ` Javier Martinez Canillas
2023-06-07 9:00 ` Javier Martinez Canillas
2023-06-05 14:47 ` [PATCH 13/30] fbdev/metronomefb: Use hardware device for dev_err() Thomas Zimmermann
2023-06-05 14:47 ` Thomas Zimmermann
2023-06-07 9:01 ` Javier Martinez Canillas
2023-06-07 9:01 ` Javier Martinez Canillas
2023-06-05 14:47 ` [PATCH 14/30] fbdev/nvidiafb: Reorder backlight and framebuffer init/cleanup Thomas Zimmermann
2023-06-05 14:47 ` Thomas Zimmermann
2023-06-07 9:02 ` Javier Martinez Canillas
2023-06-07 9:02 ` Javier Martinez Canillas
2023-06-05 14:47 ` [PATCH 15/30] fbdev/nvidiafb: Use hardware device as backlight parent Thomas Zimmermann
2023-06-05 14:47 ` Thomas Zimmermann
2023-06-07 9:02 ` Javier Martinez Canillas
2023-06-07 9:02 ` Javier Martinez Canillas
2023-06-05 14:47 ` [PATCH 16/30] fbdev/pxa168fb: Do not assign to struct fb_info.dev Thomas Zimmermann
2023-06-05 14:47 ` Thomas Zimmermann
2023-06-07 9:09 ` Javier Martinez Canillas
2023-06-07 9:09 ` Javier Martinez Canillas
2023-06-05 14:47 ` [PATCH 17/30] fbdev/radeonfb: Reorder backlight and framebuffer cleanup Thomas Zimmermann
2023-06-05 14:47 ` Thomas Zimmermann
2023-06-07 9:09 ` Javier Martinez Canillas
2023-06-07 9:09 ` Javier Martinez Canillas
2023-06-05 14:48 ` [PATCH 18/30] fbdev/radeonfb: Use hardware device as backlight parent Thomas Zimmermann
2023-06-05 14:48 ` Thomas Zimmermann
2023-06-06 5:28 ` Dan Carpenter
2023-06-06 5:28 ` Dan Carpenter
2023-06-06 7:30 ` Thomas Zimmermann
2023-06-06 7:30 ` Thomas Zimmermann
2023-06-07 9:10 ` Javier Martinez Canillas
2023-06-07 9:10 ` Javier Martinez Canillas
2023-06-05 14:48 ` [PATCH 19/30] fbdev/rivafb: Reorder backlight and framebuffer init/cleanup Thomas Zimmermann
2023-06-05 14:48 ` Thomas Zimmermann
2023-06-07 9:11 ` Javier Martinez Canillas
2023-06-05 14:48 ` [PATCH 20/30] fbdev/rivafb: Use hardware device as backlight parent Thomas Zimmermann
2023-06-05 14:48 ` Thomas Zimmermann
2023-06-07 9:11 ` Javier Martinez Canillas
2023-06-07 9:11 ` Javier Martinez Canillas
2023-06-05 14:48 ` [PATCH 21/30] fbdev/sm501fb: Output message with fb_err() Thomas Zimmermann
2023-06-05 14:48 ` Thomas Zimmermann
2023-06-07 9:12 ` Javier Martinez Canillas
2023-06-05 14:48 ` [PATCH 22/30] fbdev/smscufx: Detect registered fb_info from refcount Thomas Zimmermann
2023-06-05 14:48 ` Thomas Zimmermann
2023-06-07 22:22 ` Javier Martinez Canillas
2023-06-07 22:22 ` Javier Martinez Canillas
2023-06-12 10:19 ` Thomas Zimmermann
2023-06-12 10:40 ` Javier Martinez Canillas [this message]
2023-06-05 14:48 ` [PATCH 23/30] fbdev/tdfxfb: Set i2c adapter parent to hardware device Thomas Zimmermann
2023-06-05 14:48 ` Thomas Zimmermann
2023-06-07 22:23 ` Javier Martinez Canillas
2023-06-07 22:23 ` Javier Martinez Canillas
2023-06-05 14:48 ` [PATCH 24/30] fbdev/core: Pass Linux device to pm_vt_switch_*() functions Thomas Zimmermann
2023-06-05 14:48 ` Thomas Zimmermann
2023-06-07 19:25 ` Sam Ravnborg
2023-06-07 19:25 ` Sam Ravnborg
2023-06-05 14:48 ` [PATCH 25/30] fbdev/core: Move framebuffer and backlight helpers into separate files Thomas Zimmermann
2023-06-05 14:48 ` Thomas Zimmermann
2023-06-07 19:38 ` Sam Ravnborg
2023-06-07 19:38 ` Sam Ravnborg
2023-06-09 7:19 ` Thomas Zimmermann
2023-06-09 7:19 ` Thomas Zimmermann
2023-06-05 14:48 ` [PATCH 26/30] fbdev/core: Add fb_device_{create,destroy}() Thomas Zimmermann
2023-06-05 14:48 ` Thomas Zimmermann
2023-06-07 19:45 ` Sam Ravnborg
2023-06-07 19:45 ` Sam Ravnborg
2023-06-05 14:48 ` [PATCH 27/30] fbdev/core: Move procfs code to separate file Thomas Zimmermann
2023-06-05 14:48 ` Thomas Zimmermann
2023-06-07 20:33 ` Sam Ravnborg
2023-06-07 20:33 ` Sam Ravnborg
2023-06-05 14:48 ` [PATCH 28/30] fbdev/core: Move file-I/O code into " Thomas Zimmermann
2023-06-05 14:48 ` Thomas Zimmermann
2023-06-05 21:35 ` kernel test robot
2023-06-05 21:35 ` kernel test robot
2023-06-07 20:48 ` Sam Ravnborg
2023-06-07 20:48 ` Sam Ravnborg
2023-06-12 10:35 ` Thomas Zimmermann
2023-06-12 10:35 ` Thomas Zimmermann
2023-06-07 22:28 ` Javier Martinez Canillas
2023-06-07 22:28 ` Javier Martinez Canillas
2023-06-05 14:48 ` [PATCH 29/30] fbdev/core: Rework fb init code Thomas Zimmermann
2023-06-05 14:48 ` Thomas Zimmermann
2023-06-07 20:51 ` Sam Ravnborg
2023-06-07 20:51 ` Sam Ravnborg
2023-06-05 14:48 ` [PATCH 30/30] fbdev: Make support for userspace interfaces configurable Thomas Zimmermann
2023-06-05 14:48 ` Thomas Zimmermann
2023-06-05 15:03 ` Greg KH
2023-06-05 15:03 ` Greg KH
2023-06-05 21:45 ` kernel test robot
2023-06-05 21:45 ` kernel test robot
2023-06-07 8:48 ` Geert Uytterhoeven
2023-06-07 8:48 ` Geert Uytterhoeven
2023-06-07 15:15 ` Thomas Zimmermann
2023-06-07 15:15 ` Thomas Zimmermann
2023-06-07 15:24 ` Geert Uytterhoeven
2023-06-07 15:24 ` Geert Uytterhoeven
2023-06-07 23:07 ` Javier Martinez Canillas
2023-06-07 23:07 ` Javier Martinez Canillas
2023-06-09 7:09 ` Thomas Zimmermann
2023-06-09 7:09 ` Thomas Zimmermann
2023-06-09 7:29 ` Geert Uytterhoeven
2023-06-09 7:29 ` Geert Uytterhoeven
2023-06-09 8:00 ` Thomas Zimmermann
2023-06-09 8:00 ` Thomas Zimmermann
2023-06-09 9:14 ` Geert Uytterhoeven
2023-06-09 9:14 ` Geert Uytterhoeven
2023-06-09 11:04 ` Thomas Zimmermann
2023-06-09 11:04 ` Thomas Zimmermann
2023-06-09 11:22 ` Geert Uytterhoeven
2023-06-09 11:22 ` Geert Uytterhoeven
2023-06-09 9:59 ` Javier Martinez Canillas
2023-06-09 9:59 ` Javier Martinez Canillas
2023-06-09 10:10 ` Geert Uytterhoeven
2023-06-09 10:10 ` Geert Uytterhoeven
2023-06-09 10:24 ` Javier Martinez Canillas
2023-06-09 10:24 ` Javier Martinez Canillas
2023-06-09 11:27 ` Javier Martinez Canillas
2023-06-09 11:27 ` Javier Martinez Canillas
2023-06-11 16:37 ` Sam Ravnborg
2023-06-11 16:37 ` Sam Ravnborg
2023-06-12 6:47 ` Thomas Zimmermann
2023-06-12 6:47 ` Thomas Zimmermann
2023-06-12 7:00 ` Thomas Zimmermann
2023-06-12 7:00 ` Thomas Zimmermann
2023-06-07 8:35 ` [PATCH 00/30] fbdev: Make userspace interfaces optional Geert Uytterhoeven
2023-06-07 8:35 ` Geert Uytterhoeven
2023-06-12 10:46 ` Thomas Zimmermann
2023-06-12 10:46 ` Thomas Zimmermann
2023-06-07 12:06 ` Markus Elfring
2023-06-07 12:06 ` Markus Elfring
2023-06-07 12:21 ` Thomas Zimmermann
2023-06-07 12:21 ` Thomas Zimmermann
2023-06-07 14:08 ` Markus Elfring
2023-06-07 14:08 ` Markus Elfring
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