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 75FF1D1AD5E for ; Wed, 16 Oct 2024 13:51:09 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id E784610E70A; Wed, 16 Oct 2024 13:51:08 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (1024-bit key; unprotected) header.d=collabora.com header.i=erik.faye-lund@collabora.com header.b="L9y6QOtZ"; dkim-atps=neutral Received: from sender4-op-o10.zoho.com (sender4-op-o10.zoho.com [136.143.188.10]) by gabe.freedesktop.org (Postfix) with ESMTPS id 2503010E70A for ; Wed, 16 Oct 2024 13:51:07 +0000 (UTC) ARC-Seal: i=1; a=rsa-sha256; t=1729086660; cv=none; d=zohomail.com; s=zohoarc; b=XOBDpFWf96pcUWrMjW6umGFGhBsC/mA7961FRGSeStDyYoEA3MGj6CddpDIyqp+YWkNHk2ZqCcX7qVvzVl5IgnWSdFYimJvWZiUnGw03IN6bOrDq2/Lg3bOpjCI/ImLVn/pMig00DVvdVtltghR09e13YASKFSAJfZJ1Rh9mY/0= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1729086660; h=Content-Type:Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:In-Reply-To:MIME-Version:Message-ID:References:Subject:Subject:To:To:Message-Id:Reply-To; bh=W4BbNuxWHkxAZpAHutKfJ6e2/XQiEilqV2sXY6EC67E=; b=ATD0V41FbBm/5yFPSm0D6akI9sPFDzGV1HBcuygy6sI63PjUOr3ZFsdp87ZMjP3Checu1bF3Lp9FQGUmiHhRPHnPUTS7S3/BDXmYxrOJu06JCAvpk4msCwDlzlOen5tHckt3ZuYadaJmXXFyhkwX25QrkqnVuLWUND0zWf/NkcM= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass header.i=collabora.com; spf=pass smtp.mailfrom=erik.faye-lund@collabora.com; dmarc=pass header.from= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; t=1729086660; s=zohomail; d=collabora.com; i=erik.faye-lund@collabora.com; h=Message-ID:Subject:Subject:From:From:To:To:Cc:Cc:Date:Date:In-Reply-To:References:Content-Type:Content-Transfer-Encoding:MIME-Version:Message-Id:Reply-To; bh=W4BbNuxWHkxAZpAHutKfJ6e2/XQiEilqV2sXY6EC67E=; b=L9y6QOtZ80AnuCKlYMQMDyKfM5ZduGGbYmMRQXYuwGSkFZR5GEQb2f8xa2NA1gir DqDFDCiHHHuyu056wAa5fBdsBAqicgVzbS9wUZn4BKehqdHfmDLrkx8VPL/8xWjEPKG fvJV4x07fu/TKPKZAVfMy+Hb1bwfOKtgsUcfx3fk= Received: by mx.zohomail.com with SMTPS id 1729086659264725.0178944186945; Wed, 16 Oct 2024 06:50:59 -0700 (PDT) Message-ID: <1bd37b18455607b709529c8def963c4561e2ff1e.camel@collabora.com> Subject: Re: [PATCH v6 01/14] drm/panthor: Add uAPI From: Erik Faye-Lund To: Boris Brezillon , dri-devel@lists.freedesktop.org Cc: Daniel Stone , Liviu Dudau , Steven Price , Robin Murphy , kernel@collabora.com, Chris Diamand , Ketil Johnsen Date: Wed, 16 Oct 2024 15:50:55 +0200 In-Reply-To: <64ff75ddede7623c16ed0272eef5e950ae34e7d5.camel@collabora.com> References: <20240229162230.2634044-1-boris.brezillon@collabora.com> <20240229162230.2634044-2-boris.brezillon@collabora.com> <64ff75ddede7623c16ed0272eef5e950ae34e7d5.camel@collabora.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.54.0 (by Flathub.org) MIME-Version: 1.0 X-ZohoMailClient: External 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, 2024-10-16 at 15:16 +0200, Erik Faye-Lund wrote: > On Thu, 2024-02-29 at 17:22 +0100, Boris Brezillon wrote: > > +/** > > + * enum drm_panthor_sync_op_flags - Synchronization operation > > flags. > > + */ > > +enum drm_panthor_sync_op_flags { > > + /** @DRM_PANTHOR_SYNC_OP_HANDLE_TYPE_MASK: Synchronization > > handle type mask. */ > > + DRM_PANTHOR_SYNC_OP_HANDLE_TYPE_MASK =3D 0xff, > > + > > + /** @DRM_PANTHOR_SYNC_OP_HANDLE_TYPE_SYNCOBJ: > > Synchronization object type. */ > > + DRM_PANTHOR_SYNC_OP_HANDLE_TYPE_SYNCOBJ =3D 0, > > + > > + /** > > + * @DRM_PANTHOR_SYNC_OP_HANDLE_TYPE_TIMELINE_SYNCOBJ: > > Timeline synchronization > > + * object type. > > + */ > > + DRM_PANTHOR_SYNC_OP_HANDLE_TYPE_TIMELINE_SYNCOBJ =3D 1, > > + > > + /** @DRM_PANTHOR_SYNC_OP_WAIT: Wait operation. */ > > + DRM_PANTHOR_SYNC_OP_WAIT =3D 0 << 31, > > + > > + /** @DRM_PANTHOR_SYNC_OP_SIGNAL: Signal operation. */ > > + DRM_PANTHOR_SYNC_OP_SIGNAL =3D (int)(1u << 31), >=20 > Why do we cast to int here? 1u << 31 doesn't fit in a 32-bit signed > integer, so isn't this undefined behavior in C? >=20 Seems this was proposed here: https://lore.kernel.org/dri-devel/89be8f8f-7c4e-4efd-0b7b-c30bcfbf1d23@arm.= com/ ...that kinda sounds like bad advice to me. Also, it's been pointed out to me elsewhere that this isn't *technically speaking* undefined, it's "implementation defined". But as far as kernel interfaces goes, that's pretty much the same; we can't guarantee that the kernel and the user-space is using the same implementation. Here's the quote from the C99 spec, section 6.3.1.3 "Signed and unsigned integers": """ Otherwise, the new type is signed and the value cannot be represented in it; either the result is implementation-defined or an implementation-defined signal is raised """" I think a better approach be to use -1 << 31, which is well-defined. But the problem then becomes assigning it into drm_panthor_sync_op::flags in a well-defined way... Could we make the field signed? That seems a bit bad as well...