From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from fanzine2.igalia.com (fanzine.igalia.com [178.60.130.6]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 60232137745 for ; Sat, 13 Jul 2024 14:45:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=178.60.130.6 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720881943; cv=none; b=L9PPxtvUfYNAgy7iOc8f9c9+KRYo7obdZQ2rH187VOXKvCvDLlgxyCKuThMOEUXuxT1WZPAlJZScI9VOxDgXWwXWn3JESRH/9Oe3nIm4Y7odtq2a+T+IpUaayiFXWnTphrEGIEvYXZR+IBG8JnF4JG6mAZIr9oJCQyF7LHPh1XQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720881943; c=relaxed/simple; bh=f9bxnKUQzD8IO05M6SagpxSAdI9jsfJPkop6KCwz2q4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=FaBclbiAAaPGCgm9sXEzjwApUgCs2LKEx35wdfdc54GBWcywRF29ulveZvUvXQ+xdv1WI//uqAvsXwHvFOg6tU8/cPQJIVP0zujJRNosasrjqE/qeVP/0/FUsRR3naNosWlWDwwMELBS48vqg5FUxICblbScOZioKwztE7xG2nU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=igalia.com; spf=pass smtp.mailfrom=igalia.com; dkim=pass (2048-bit key) header.d=igalia.com header.i=@igalia.com header.b=M2prIyWB; arc=none smtp.client-ip=178.60.130.6 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=igalia.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=igalia.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=igalia.com header.i=@igalia.com header.b="M2prIyWB" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=igalia.com; s=20170329; h=Content-Transfer-Encoding:Content-Type:In-Reply-To:From: References:Cc:To:Subject:MIME-Version:Date:Message-ID:Sender:Reply-To: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=CXyAMCJYhNH9e3PTxvXhtZsKyPJujdEq3lz2SA/wbZo=; b=M2prIyWBm8mP4jeOjSivfDbJc0 1RP8S8t738XgbnzzaT2kEIDvd5GXpzz9NYcYxdZRHMJc/1xpgRBdBDeyd6F1tvKGMPD3/JkcAvVQL SNp/so/BYAoOakyWVmfwDVB46G5B6ptDlx468bwPgjr5SYzUlDWqqGrLO+LhurXlN8UtKp9xt+qtq W2MtfPDy8FviwZ04QiRmUSjl2Zd321f8530mNsCCf2AwbYcGmptwX6UNEscDy7HYpQ0PdOidouPim NImiBe//8Q9+UAcp4/yYxzmwdb58kPs+1m3Ukj97JjGkdmqTUJQo8QGZiB1bmsuUwLrqPSJNhhVVT ly2xYzGQ==; Received: from [187.36.213.55] (helo=[192.168.1.212]) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_128_GCM:128) (Exim) id 1sSe05-00EkgM-4k; Sat, 13 Jul 2024 16:45:25 +0200 Message-ID: Date: Sat, 13 Jul 2024 11:45:16 -0300 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 05/17] drm/vkms: Add dummy pixel_read/pixel_write callbacks to avoid NULL pointers To: Louis Chauvet , Rodrigo Siqueira , Melissa Wen , Haneen Mohammed , Daniel Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , rdunlap@infradead.org, arthurgrillo@riseup.net, Jonathan Corbet , pekka.paalanen@haloniitty.fi Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, jeremie.dautheribes@bootlin.com, miquel.raynal@bootlin.com, thomas.petazzoni@bootlin.com, seanpaul@google.com, marcheu@google.com, nicolejadeyee@google.com, Pekka Paalanen References: <20240516-yuv-v8-0-cf8d6f86430e@bootlin.com> <20240516-yuv-v8-5-cf8d6f86430e@bootlin.com> Content-Language: en-US From: =?UTF-8?Q?Ma=C3=ADra_Canal?= Autocrypt: addr=mcanal@igalia.com; keydata= xjMEZIsaeRYJKwYBBAHaRw8BAQdAGU6aY8oojw61KS5rGGMrlcilFqR6p6ID45IZ6ovX0h3N H01haXJhIENhbmFsIDxtY2FuYWxAaWdhbGlhLmNvbT7CjwQTFggANxYhBDMCqFtIvFKVRJZQ hDSPnHLaGFVuBQJkixp5BQkFo5qAAhsDBAsJCAcFFQgJCgsFFgIDAQAACgkQNI+cctoYVW5u GAEAwpaC5rI3wD8zqETKwGVoXd6+AbmGfZuVD40xepy7z/8BAM5w95/oyPsHUqOsg/xUTlNp rlbhA+WWoaOXA3XgR+wCzjgEZIsaeRIKKwYBBAGXVQEFAQEHQGoOK0jgh0IorMAacx6WUUWb s3RLiJYWUU6iNrk5wWUbAwEIB8J+BBgWCAAmFiEEMwKoW0i8UpVEllCENI+cctoYVW4FAmSL GnkFCQWjmoACGwwACgkQNI+cctoYVW6cqwD/Q9R98msvkhgRvi18fzUPFDwwogn+F+gQJJ6o pwpgFkAA/R2zOfla3IT6G3SBoV5ucdpdCpnIXFpQLbmfHK7dXsAC In-Reply-To: <20240516-yuv-v8-5-cf8d6f86430e@bootlin.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 5/16/24 10:04, Louis Chauvet wrote: > Introduce two callbacks which does nothing. They are used in replacement > of NULL and it avoid kernel OOPS if this NULL is called. I don't believe we should avoid a reasonable kernel OOPS. As you noticed, if the user got this kernel OOPS it means that there is a mismatch between what formats are announced by atomic_check and what is really supported by atomic_update. This is a driver error. If this happens, I want the kernel OOPS because it means I need to fix the driver. Sometimes a kernel OOPS can save you some valuable debugging time. I'd probably drop this patch. Best Regards, - Maíra > > If those callback are used, it means that there is a mismatch between > what formats are announced by atomic_check and what is realy supported by > atomic_update. > > Acked-by: Pekka Paalanen > Signed-off-by: Louis Chauvet > --- > drivers/gpu/drm/vkms/vkms_formats.c | 45 ++++++++++++++++++++++++++++++++----- > 1 file changed, 39 insertions(+), 6 deletions(-) > > diff --git a/drivers/gpu/drm/vkms/vkms_formats.c b/drivers/gpu/drm/vkms/vkms_formats.c > index 6b3e17374b19..c28c32b00e39 100644 > --- a/drivers/gpu/drm/vkms/vkms_formats.c > +++ b/drivers/gpu/drm/vkms/vkms_formats.c > @@ -135,6 +135,21 @@ static void RGB565_to_argb_u16(u8 *in_pixel, struct pixel_argb_u16 *out_pixel) > out_pixel->b = drm_fixp2int_round(drm_fixp_mul(fp_b, fp_rb_ratio)); > } > > +/** > + * magenta_to_argb_u16() - pixel_read callback which always read magenta > + * > + * This callback is used when an invalid format is requested for plane reading. > + * It is used to avoid null pointer to be used as a function. In theory, this function should > + * never be called, except if you found a bug in the driver/DRM core. > + */ > +static void magenta_to_argb_u16(u8 *in_pixel, struct pixel_argb_u16 *out_pixel) > +{ > + out_pixel->a = (u16)0xFFFF; > + out_pixel->r = (u16)0xFFFF; > + out_pixel->g = 0; > + out_pixel->b = (u16)0xFFFF; > +} > + > /** > * vkms_compose_row - compose a single row of a plane > * @stage_buffer: output line with the composed pixels > @@ -237,6 +252,16 @@ static void argb_u16_to_RGB565(u8 *out_pixel, struct pixel_argb_u16 *in_pixel) > *pixel = cpu_to_le16(r << 11 | g << 5 | b); > } > > +/** > + * argb_u16_to_nothing() - pixel_write callback with no effect > + * > + * This callback is used when an invalid format is requested for writeback. > + * It is used to avoid null pointer to be used as a function. In theory, this should never > + * happen, except if there is a bug in the driver > + */ > +static void argb_u16_to_nothing(u8 *out_pixel, struct pixel_argb_u16 *in_pixel) > +{} > + > /** > * vkms_writeback_row() - Generic loop for all supported writeback format. It is executed just > * after the blending to write a line in the writeback buffer. > @@ -260,8 +285,10 @@ void vkms_writeback_row(struct vkms_writeback_job *wb, > > /** > * get_pixel_conversion_function() - Retrieve the correct read_pixel function for a specific > - * format. The returned pointer is NULL for unsupported pixel formats. The caller must ensure that > - * the pointer is valid before using it in a vkms_plane_state. > + * format. > + * > + * If the format is not supported by VKMS a warning is emitted and a dummy "always read magenta" > + * function is returned. > * > * @format: DRM_FORMAT_* value for which to obtain a conversion function (see [drm_fourcc.h]) > */ > @@ -284,18 +311,21 @@ pixel_read_t get_pixel_read_function(u32 format) > * format must: > * - Be listed in vkms_formats in vkms_plane.c > * - Have a pixel_read callback defined here > + * > + * To avoid kernel crash, a dummy "always read magenta" function is used. It means > + * that during the composition, this plane will always be magenta. > */ > WARN(true, > "Pixel format %p4cc is not supported by VKMS planes. This is a kernel bug, atomic check must forbid this configuration.\n", > &format); > - return (pixel_read_t)NULL; > + return &magenta_to_argb_u16; > } > } > > /** > * get_pixel_write_function() - Retrieve the correct write_pixel function for a specific format. > - * The returned pointer is NULL for unsupported pixel formats. The caller must ensure that the > - * pointer is valid before using it in a vkms_writeback_job. > + * If the format is not supported by VKMS a warning is emitted and a dummy "don't do anything" > + * function is returned. > * > * @format: DRM_FORMAT_* value for which to obtain a conversion function (see [drm_fourcc.h]) > */ > @@ -318,10 +348,13 @@ pixel_write_t get_pixel_write_function(u32 format) > * format must: > * - Be listed in vkms_wb_formats in vkms_writeback.c > * - Have a pixel_write callback defined here > + * > + * To avoid kernel crash, a dummy "don't do anything" function is used. It means > + * that the resulting writeback buffer is not composed and can contains any values. > */ > WARN(true, > "Pixel format %p4cc is not supported by VKMS writeback. This is a kernel bug, atomic check must forbid this configuration.\n", > &format); > - return (pixel_write_t)NULL; > + return &argb_u16_to_nothing; > } > } >