From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 8F1D113DDD2; Tue, 18 Jun 2024 21:38:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718746715; cv=none; b=ZPOA3DDpjnEgpukP7SZTr41RheMFMVXpvaCHrr1JEua3wNG03lCuXwuFCzv02RH6HwOBQzWJGpmM4I9jPvSZ2/G/0mkjjmrjhKpgvJXzIjrZ6H60uxU32iZBMB2lGEQk1dUjLJR7PKtTUuPjyp82UPd9GXYPVFGakjCBUqFIKT0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718746715; c=relaxed/simple; bh=AYq7euI/XVOdUL29dkH24ZxEpRRBcB8uSdj9EW0Rmrc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ET/0u0Aw7YUHIKRVM1kVNuF7Ekz7CVfvb+sWxbW+C3ROSGrtVCAGBEw9UFEeLk6805Babvr8AllRXZ2Iana4v66T1kmoemJW03dY3IiWtem9FK8ixLBSyGnNcCKaL4L0/aCCd2NqhgTdB129mycp9tqCGj69yFpARwDWTwr5WR0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1613BC3277B; Tue, 18 Jun 2024 21:38:31 +0000 (UTC) Date: Tue, 18 Jun 2024 22:38:29 +0100 From: Catalin Marinas To: Baruch Siach Cc: Christoph Hellwig , Marek Szyprowski , Rob Herring , Saravana Kannan , Will Deacon , Robin Murphy , iommu@lists.linux.dev, devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, Petr =?utf-8?B?VGVzYcWZw61r?= , Ramon Fried , Elad Nachman Subject: Re: [PATCH RFC v2 2/5] of: get dma area lower limit Message-ID: References: <230ea13ef8e9f576df849e1b03406184ca890ba8.1712642324.git.baruch@tkos.co.il> Precedence: bulk X-Mailing-List: devicetree@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: <230ea13ef8e9f576df849e1b03406184ca890ba8.1712642324.git.baruch@tkos.co.il> On Tue, Apr 09, 2024 at 09:17:55AM +0300, Baruch Siach wrote: > of_dma_get_max_cpu_address() returns the highest CPU address that > devices can use for DMA. The implicit assumption is that all CPU > addresses below that limit are suitable for DMA. However the > 'dma-ranges' property this code uses also encodes a lower limit for DMA > that is potentially non zero. > > Rename to of_dma_get_cpu_limits(), and extend to retrieve also the lower > limit for the same 'dma-ranges' property describing the high limit. I don't understand the reason for the lower limit. The way the Linux zones work is that ZONE_DMA always starts from the start of the RAM. It doesn't matter whether it's 0 or not, you'd not allocate below the start of RAM anyway. If you have a device that cannot use the bottom of the RAM, it is pretty broken and not supported by Linux. I think you added this limit before we tried to move away from zone_dma_bits to a non-power-of-two limit (zone_dma_limit). With the latter, we no longer need tricks with the lower limit, of_dma_get_max_cpu_address() should capture the smallest upper CPU address limit supported by all devices (and that's where ZONE_DMA should end). -- Catalin