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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6FDFBC433FE for ; Mon, 10 Jan 2022 17:33:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238382AbiAJRdg (ORCPT ); Mon, 10 Jan 2022 12:33:36 -0500 Received: from bhuna.collabora.co.uk ([46.235.227.227]:39700 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237928AbiAJRdf (ORCPT ); Mon, 10 Jan 2022 12:33:35 -0500 Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: alyssa) with ESMTPSA id D1F011F41363 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1641836013; bh=2g3G8luaz7ZD7KDtSA8vvM2OkKCtTnXdaPyiMq/li4o=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=UUtwoWJQolaU0Y8Or88wO8xZP6aNj7MXNPv1KLki5CEg0FiL44bsKgx9JH3QvzYYg 0lMJE9zIaycVkZLoIhKxVd8rAlg/lPVlLARElU4XY1DleVdOkPp7iCNVgYC7W6cev2 UWKC8NQeQ4OM8hjYQT4fdzJHiTtmoCE/YFwOjjp/qk5PGuoIIA40wnp2eIULDmSq2g NHUBV7v8JZCEgeaxIMCQxHYEkV3GF+V5O0WPCSEQX8ZLW1JLGlrk9TOhHG29TihYXt P+jpmKlYZPMSRtFRB6m786ephM1jURVLKKzjZDVzxy9hqF6r8wWD9PoDZIY9KaIjnX oDohSMgKlus5Q== Date: Mon, 10 Jan 2022 12:33:26 -0500 From: Alyssa Rosenzweig To: Steven Price Cc: Alyssa Rosenzweig , dri-devel@lists.freedesktop.org, Rob Herring , Tomeu Vizoso , David Airlie , Daniel Vetter , linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH] drm/panfrost: Handle IDVS_GROUP_SIZE feature Message-ID: References: <20220109171254.3183-1-alyssa.rosenzweig@collabora.com> <4628eb5a-b644-47af-a865-73300460a92b@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4628eb5a-b644-47af-a865-73300460a92b@arm.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > This feature adds an extra IDVS group size field to the JM_CONFIG > > register. In kbase, the value is configurable via the device tree; kbase > > uses 0xF as a default if no value is specified. Until we find a device > > demanding otherwise, let's always set the 0xF default on devices which > > support this feature mimicking kbase's behaviour. > > This is a performance thing - so I don't think it will break anything if > this is wrong, it just won't be optimal. Then interpret my remarks as hardcoding the default until we find a device where setting to something other than 0xF improves performance nontrivially. (Read: I am lazy and do not want to write dt-bindings for something nobody will ever use.) > > As JM_CONFIG is an undocumented register, it's not clear to me what > > happens if we fail to include this handling. Index-driven vertex shading > > already works on Bifrost boards with this feature without this handling. > > Perhaps this has performance implications? Patch untested for the > > moment, wanted to give Steven a chance to comment. > > As it's a performance thing you shouldn't see correctness issues with > not setting it. But 0xF seems to have been chosen as it gave the best > overall performance (although for individual test content this can > vary). AFAICT the performance impact isn't massive either. Good to know, will update the commit message accordingly. > Reviewed-by: Steven Price > > Since you've tagged this RFC I won't merge it now, but it looks correct > to me. Thanks for the review... I hope you like reviewing Panfrost patches because I have a Valhall bring-up series waiting o:) When I get a chance to uprev the kernel on my G52 board I'll see if I can benchmark the impact of this change, so far this is only compile-tested. Even if there's no impact the patch should likely go in to stay consistent with kbase, but hopefully there's a win from this. At that point I'll send a v2 with your reviewed-by (and hopefully no changes other than the commit message) and we'll land that.