Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <b7d937bc-d7c3-6f7a-047c-fc6e5756a5a0@redhat.com>
Date:   Fri, 8 Jul 2022 21:28:32 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.8.0
Subject: Re: [PATCH 1/5] drm/modes: parse_cmdline: Handle empty mode name part
Content-Language: en-US
To:     Geert Uytterhoeven <geert@linux-m68k.org>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>
Cc:     dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org,
        linux-m68k@vger.kernel.org, linux-kernel@vger.kernel.org
References: <cover.1657301107.git.geert@linux-m68k.org>
 <64e2e9b14c26df28908789374253fd12072c26c2.1657301107.git.geert@linux-m68k.org>
From:   Hans de Goede <hdegoede@redhat.com>
In-Reply-To: <64e2e9b14c26df28908789374253fd12072c26c2.1657301107.git.geert@linux-m68k.org>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

Hi Geert,

On 7/8/22 20:21, Geert Uytterhoeven wrote:
> If no mode name part was specified, mode_end is zero, and the "ret ==
> mode_end" check does the wrong thing.
> 
> Fix this by checking for a non-zero return value instead.

Which is wrong to do, since now if you have e.g. a mode list
with:

"dblntsc",
"dblntsc-ff"

in there and the cmdline contains "dblntsc-ff" then you
will already stop with a (wrong!) match at "dblntsc".

> While at it, skip all named mode handling when mode_end is zero, as it
> is futile.

AFAICT, this is actually what needs to be done to fix this, while keeping
the ret == mode_end check.

Regards,

Hans


> 
> Fixes: 7b1cce760afe38b4 ("drm/modes: parse_cmdline: Allow specifying stand-alone options")
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> ---
>  drivers/gpu/drm/drm_modes.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
> index 14b746f7ba975954..30a7be97707bfb16 100644
> --- a/drivers/gpu/drm/drm_modes.c
> +++ b/drivers/gpu/drm/drm_modes.c
> @@ -1823,9 +1823,9 @@ bool drm_mode_parse_command_line_for_connector(const char *mode_option,
>  	}
>  
>  	/* First check for a named mode */
> -	for (i = 0; i < ARRAY_SIZE(drm_named_modes_whitelist); i++) {
> +	for (i = 0; mode_end && i < ARRAY_SIZE(drm_named_modes_whitelist); i++) {
>  		ret = str_has_prefix(name, drm_named_modes_whitelist[i]);
> -		if (ret == mode_end) {
> +		if (ret) {
>  			if (refresh_ptr)
>  				return false; /* named + refresh is invalid */
>