Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932095AbdDFShr (ORCPT ); Thu, 6 Apr 2017 14:37:47 -0400 Received: from mail-io0-f195.google.com ([209.85.223.195]:32932 "EHLO mail-io0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752436AbdDFShi (ORCPT ); Thu, 6 Apr 2017 14:37:38 -0400 Subject: Re: [PATCH] of: change fixup of dma-ranges size to error To: Rob Herring References: <1491459529-31391-1-git-send-email-frowand.list@gmail.com> Cc: "devicetree@vger.kernel.org" , "linux-kernel@vger.kernel.org" From: Frank Rowand Message-ID: <58E68ADC.6040603@gmail.com> Date: Thu, 6 Apr 2017 11:37:16 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2180 Lines: 52 On 04/06/17 07:03, Rob Herring wrote: > On Thu, Apr 6, 2017 at 1:18 AM, wrote: >> From: Frank Rowand >> >> of_dma_get_range() has workaround code to fixup a device tree that >> incorrectly specified a mask instead of a size for property >> dma-ranges. That device tree was fixed a year ago in v4.6, so >> the workaround is no longer needed. Leave a data validation >> check in place, but no longer do the fixup. Move the check >> one level deeper in the call stack so that other possible users >> of dma-ranges will also be protected. >> >> The fix to the device tree was in >> commit c91cb9123cdd ("dtb: amd: Fix DMA ranges in device tree"). > > NACK. > This was by design. You can't represent a size of 2^64 or 2^32. I agree that being unable to represent a size of 2^32 in a u32 and a size of 2^64 in a u64 is the underlying issue. But the code to convert a mask to a size is _not_ design, it is a hack that temporarily worked around a device tree that did not follow the dma-ranges binding in the ePAPR. That device tree was corrected a year ago to provide a size instead of a mask. > Well, technically you can for the latter, but then you have to grow > #size-cells to 2 for an otherwise all 32-bit system which seems kind > of pointless and wasteful. You could further restrict this to only > allow ~0 and not just any case with bit 0 set. > > I'm pretty sure AMD is not the only system. There were 32-bit systems too. I examined all instances of property dma-ranges in in tree dts files in Linux 4.11-rc1. There are none that incorrectly specify mask instead of size. #size-cells only changes to 2 for the dma-ranges property and the ranges property when size is 2^32, so that is a very small amount of space. The patch does not allow for a size of 2^64. If a system requires a size of 2^64 then the type of size needs to increase to be larger than a u64. If you would like for the code to be defensive and detect a device tree providing a size of 2^64 then I can add a check to of_dma_get_range() to return -EINVAL if #size-cells > 2. When that error triggers, the type of size can be changed. > > Rob >