From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id EA43610775E0 for ; Wed, 18 Mar 2026 16:07:00 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 4C62510E040; Wed, 18 Mar 2026 16:07:00 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=collabora.com header.i=@collabora.com header.b="MXWBMUgb"; dkim-atps=neutral Received: from bali.collaboradmins.com (bali.collaboradmins.com [148.251.105.195]) by gabe.freedesktop.org (Postfix) with ESMTPS id F3E3910E040 for ; Wed, 18 Mar 2026 16:06:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1773850016; bh=/BZhzcK4gj7iAcnIws8JWOideBOmHSDSiVdZIqnxQcs=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=MXWBMUgbhkX/X9qDeh8WEmIZx+Lx0tsXoleF6FJE36xAAYEPm9hgxAff8bfR8+U/P 9hJ+s1JFVri5d6pzAuY7CREcGMvpMZ3B9n+/LlQg10et6V7v1ig8jmkcUg8ZAkxtCW IJgydeclx2n5xmivAm1airPDiaYAnL4y1qIis2FOzKr8dvBH5NMeHca0hYNAdsqgha TpjrNP/OR9AVqz6V8poEoVGyhPEFM7PkGBE0aACXiwWrTYvleBnRQMZ5i9bWABuFYS 3vLGwl/AL7z6jaE7PJLwwx/u9E1h+AFsfvaiCty+VItB91nIXgc4dS+vdni/3lqfaN 9FUlBxzqDBanw== Received: from fedora (unknown [IPv6:2a01:e0a:2c:6930:d919:a6e:5ea1:8a9f]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (prime256v1) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: bbrezillon) by bali.collaboradmins.com (Postfix) with ESMTPSA id 12E4017E1005; Wed, 18 Mar 2026 17:06:56 +0100 (CET) Date: Wed, 18 Mar 2026 17:06:50 +0100 From: Boris Brezillon To: Steven Price Cc: Marcin =?UTF-8?B?xZpsdXNhcno=?= , Liviu Dudau , dri-devel@lists.freedesktop.org, Chia-I Wu , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Lukas Zapolskas , nd@arm.com Subject: Re: [PATCH] drm/panthor: extend timestamp query with flags Message-ID: <20260318170650.496872ae@fedora> In-Reply-To: <72a93cdd-b105-41aa-bf12-d6caf7e90078@arm.com> References: <20260318112952.645160-1-marcin.slusarz@arm.com> <20260318131030.4ae7f820@fedora> <72a93cdd-b105-41aa-bf12-d6caf7e90078@arm.com> Organization: Collabora X-Mailer: Claws Mail 4.3.1 (GTK 3.24.51; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Wed, 18 Mar 2026 15:20:18 +0000 Steven Price wrote: > On 18/03/2026 14:51, Marcin =C5=9Alusarz wrote: > > On Wed, Mar 18, 2026 at 01:10:30PM +0100, Boris Brezillon wrote: =20 > >> On Wed, 18 Mar 2026 12:29:52 +0100 > >> Marcin Slusarz wrote: > >> =20 > >>> Flags now control which data user space wants to query, > >>> there is more information sources, and there's ability > >>> to query duration of multiple timestamp reads. > >>> > >>> New sources: > >>> - CPU's monotonic, > >>> - CPU's monotonic raw, > >>> - GPU's cycle count > >>> > >>> These changes should make the implementation of > >>> VK_KHR_calibrated_timestamps more accurate and much simpler. > >>> > >>> Signed-off-by: Marcin Slusarz > >>> --- > >>> This is counter proposal to https://lore.kernel.org/all/2025091620075= 1.3999354-1-olvaffe@gmail.com/ > >>> --- > >>> drivers/gpu/drm/panthor/panthor_drv.c | 124 ++++++++++++++++++++++++= -- > >>> include/uapi/drm/panthor_drm.h | 51 ++++++++++- > >>> 2 files changed, 166 insertions(+), 9 deletions(-) > >>> > >>> diff --git a/drivers/gpu/drm/panthor/panthor_drv.c b/drivers/gpu/drm/= panthor/panthor_drv.c > >>> index 165dddfde6ca..19ede20a578e 100644 > >>> --- a/drivers/gpu/drm/panthor/panthor_drv.c > >>> +++ b/drivers/gpu/drm/panthor/panthor_drv.c > >>> @@ -13,7 +13,9 @@ > >>> #include > >>> #include > >>> #include > >>> +#include > >>> #include > >>> +#include > >>> =20 > >>> #include > >>> #include > >>> @@ -762,21 +764,123 @@ static void panthor_submit_ctx_cleanup(struct = panthor_submit_ctx *ctx, > >>> } > >>> =20 > >>> static int panthor_query_timestamp_info(struct panthor_device *ptdev, > >>> - struct drm_panthor_timestamp_info *arg) > >>> + struct drm_panthor_timestamp_info *arg, > >>> + u32 size) > >>> { > >>> int ret; > >>> + u32 flags; > >>> + unsigned long irq_flags; > >>> + struct timespec64 cpu_ts; > >>> + u64 query_start_time; > >>> + bool minimize_interruption; > >>> + u32 timestamp_types =3D 0; > >>> + > >>> + if (size >=3D offsetof(struct drm_panthor_timestamp_info, pad1) + s= izeof(arg->pad1) && > >>> + arg->pad1 !=3D 0) > >>> + return -EINVAL; > >>> + > >>> + if (size >=3D offsetof(struct drm_panthor_timestamp_info, flags) + = sizeof(arg->flags)) > >>> + flags =3D arg->flags; > >>> + else > >>> + flags =3D DRM_PANTHOR_TIMESTAMP_GPU | > >>> + DRM_PANTHOR_TIMESTAMP_GPU_OFFSET | > >>> + DRM_PANTHOR_TIMESTAMP_FREQ; =20 > >> > >> How about we add a DRM_PANTHOR_TIMESTAMP_ADVANCED_QUERY flag that tells > >> the driver whether the default should be picked or not instead of this > >> weird is-this-the-new-or-old-struct detection based on the size. =20 > >=20 > > Well, as is, we would read uninitialized data from kernel stack if > > user passed old struct with the original size. It's fixable, but > > I'm not sure why you think checking size to detect the use of new > > interface is weird. I thought it's a pretty standard thing. =20 >=20 > What you need is copy_struct_from_user() - it will zero any fields that > user space didn't provide. So adding a flags field to the end of the > struct will be guaranteed to be zero with old (binary of) user space. This ^. >=20 > This is the standard way of extending an API. If user space is > recompiled with new headers then user space will pass in the larger size > (because it uses sizeof()), but will zero initialise any fields that it > doesn't know about. If you look purely at the size passed by userspace > then the sizeof() will be wrong and no flags will get set. >=20 > > If the conclusion will be that checking size must be dropped, then > > I think looking at flags being non-zero would be enough - there's > > no need for new special flag that says other bits mean something. =20 >=20 > That would be fine if we don't want the 'default' flags behaviour you > have above. So either GPU/GPU_OFFSET/FREQ are unconditionally enabled or > you need to reverse the meaning of those flags. Right, if you don't want the extra ADVANCED_QUERY flag, the GPU, GPU_OFFSET and FREQ flags need to be opt-out, but that's a bit confusing if the other flags are opt-in. > Or of course go with > Boris's suggestion of a flag to enable the new behaviour. >=20 > [...] >=20 > >>> /** > >>> * struct drm_panthor_timestamp_info - Timestamp information > >>> * > >>> @@ -421,11 +450,29 @@ struct drm_panthor_timestamp_info { > >>> */ > >>> __u64 timestamp_frequency; > >>> =20 > >>> - /** @current_timestamp: The current timestamp. */ > >>> + /** @current_timestamp: The current GPU timestamp. */ > >>> __u64 current_timestamp; > >>> =20 > >>> - /** @timestamp_offset: The offset of the timestamp timer. */ > >>> + /** @timestamp_offset: The offset of the GPU timestamp timer. */ > >>> __u64 timestamp_offset; > >>> + > >>> + /** @flags: Bitmask of drm_panthor_timestamp_info_flags. */ > >>> + __u32 flags; > >>> + > >>> + /** @duration_nsec: Duration of time query. */ > >>> + __u32 duration_nsec; > >>> + > >>> + /** @cycle_count: Value of GPU_CYCLE_COUNT. */ > >>> + __u64 cycle_count; > >>> + > >>> + /** @cpu_timestamp_sec: Seconds part of CPU timestamp. */ > >>> + __u64 cpu_timestamp_sec; > >>> + > >>> + /** @cpu_timestamp_nsec: Nanseconds part of CPU timestamp. */ > >>> + __u32 cpu_timestamp_nsec; > >>> + > >>> + /** @pad1: Padding, MBZ. */ > >>> + __u32 pad1; =20 > >> > >> Let's re-purpose the existing pad field into flags, move duration_nsec= after > >> cpu_timestamp_nsec, and get rid of this pad1. =20 > >=20 > > I'm not sure I understand. Do you want me to extend flags to u64? > > What's the point of that? =20 >=20 > I'm not sure I necessarily understand Boris's comment either, but I > would suggest making flags u64 would be better. I was confused by the fact the field was named pad1, and I assumed there was a pad field already present in the struct, which is why I suggested re-purposing that one instead of adding a new field that would in turn require extra padding. Given there's no pre-existing padding, I'd rename pad1 into pad and call it a day. >=20 > By shuffling things around to have a u64 flags you no longer have any > padding fields. And the unused part of the flags will be naturally > checked for being 0 rather than the explicit check for pad1 you > currently have. >=20 > Not a big deal to me - but it's easier to just avoid padding fields > where possible as they often get overlooked in the validation. We certainly want to ensure they are, this way we can re-purpose existing padding fields instead of adding new ones when we need to extend the logic.