From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 91AFAFC0A; Thu, 4 Jul 2024 06:11:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720073506; cv=none; b=PrmBVEsa8LP+ZFuZoXlPN5quhnHUQfRpEBs3MdSA+Y+/jX359gK5r8opSAM2GWBl/br0+fM5wRlAQywOTlHn/8XwDlKLIJHz2D5v1wK18/4uL95+aqJHBGXygrofKy5Gtx8f8SPYVEcvWxzRNhBvZ2n0iVobBN8N2g6snWIv5A0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720073506; c=relaxed/simple; bh=aDrAoHB8yy2A3/CS5V0LEYqnLU6En2W4VPvbgotYtWQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=gt1QxoHVQ1dO2zx08BhX6mK76T6fH2NOAS1k4RuKhnGwT3blbsgoRndUMmeZWHE/6PEPMQjKyRL3uTjv56HqM4mKGLnawLdz7G2pW7v3MVA5+u39GGP5lc1TAPlTefC/VI6C2FTHMIwPUZWhhUxk0L+3AFlffVj7/aGl5DuN008= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=yDApkY8D; arc=none smtp.client-ip=198.137.202.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="yDApkY8D" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=wMDUzWPY2FXi8oQKbIXbNY1WdXq1Yu34joP84Ju99HM=; b=yDApkY8DoyGRO2LI2uMCseBbMd ZxIu/gRNIzhW2aiCEUL9HLLgWUh0vKkQc7KOuhp3Sfb4M4WoLC1/l0VOHKxjzP/QKOmjmtVpc0Y/x Gkt+z5Zt5zQpfLLovS5e5wwGlCx+r2U+ow8NI2KOKz0WRDk5YEoRQ3i5zcV+bEzGF1ZrJueM85m4m xDqqbL0OhOXvzofjybbyWbRoQ/gXB9WNvgUv2mb7XFnLYIFPcu3byetSz4tk5DH+xvA7wGhvgPEPq GALc7DqOAJ8kkK5ib4iDYDkZxyN0pqmLQG81BmdLBjqHF6iOYFxgCmEGIGFYeqvRGc6xM2qeADOLs mz5PiXGw==; Received: from hch by bombadil.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1sPFgz-0000000CIfu-2MUG; Thu, 04 Jul 2024 06:11:41 +0000 Date: Wed, 3 Jul 2024 23:11:41 -0700 From: Christoph Hellwig To: Icenowy Zheng Cc: Bjorn Helgaas , Jiaxun Yang , Christian =?iso-8859-1?Q?K=F6nig?= , Huang Rui , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Daniel Vetter , bhelgaas@google.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org Subject: Re: PCIe coherency in spec (was: [RFC PATCH 2/2] drm/ttm: downgrade cached to write_combined when snooping not available) Message-ID: References: <20240703210831.GA63958@bhelgaas> <99ff395019901c5c1a7b298481c8261b30fdbd01.camel@icenowy.me> Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <99ff395019901c5c1a7b298481c8261b30fdbd01.camel@icenowy.me> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html On Thu, Jul 04, 2024 at 10:00:52AM +0800, Icenowy Zheng wrote: > So I here want to ask a question as an individual hacker: what's the > policy of linux-pci towards these non-coherent PCIe implementations? > > If the sentences of Christian is right, these implementations are just > out-of-spec, should them get purged out of the kernel, or at least > raising a warning that some HW won't work because of inconformant > implementation? Nothing in the PCIe specifications that mandates a programming model. Non-coherent DMA is extremely common in lower end devices, and despite all the issues that it causes well supported in Linux. What are you trying to solve?