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[92.176.231.205]) by smtp.gmail.com with ESMTPSA id v6-20020a7bcb46000000b003f6028a4c85sm3342086wmj.16.2023.06.07.15.22.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 07 Jun 2023 15:22:44 -0700 (PDT) From: Javier Martinez Canillas To: Thomas Zimmermann , daniel@ffwll.ch, sam@ravnborg.org, deller@gmx.de, geert+renesas@glider.be, lee@kernel.org, daniel.thompson@linaro.org, jingoohan1@gmail.com Cc: linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-sh@vger.kernel.org, linux-omap@vger.kernel.org, linux-staging@lists.linux.dev, Thomas Zimmermann , Steve Glendinning Subject: Re: [PATCH 22/30] fbdev/smscufx: Detect registered fb_info from refcount In-Reply-To: <20230605144812.15241-23-tzimmermann@suse.de> References: <20230605144812.15241-1-tzimmermann@suse.de> <20230605144812.15241-23-tzimmermann@suse.de> Date: Thu, 08 Jun 2023 00:22:43 +0200 Message-ID: <87edmmewuk.fsf@minerva.mail-host-address-is-not-set> Precedence: bulk X-Mailing-List: linux-staging@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Thomas Zimmermann 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 > Cc: Steve Glendinning > --- > 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 ? But that was also the case for info->dev check, so I guess is OK and this change is for an old fbdev driver anyways. Reviewed-by: Javier Martinez Canillas -- Best regards, Javier Martinez Canillas Core Platforms Red Hat