From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752463AbbBTFCA (ORCPT ); Fri, 20 Feb 2015 00:02:00 -0500 Received: from gate.crashing.org ([63.228.1.57]:58913 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751181AbbBTFB6 (ORCPT ); Fri, 20 Feb 2015 00:01:58 -0500 Message-ID: <1424408500.27448.25.camel@kernel.crashing.org> Subject: Concerns about "mpt2sas: Added Reply Descriptor Post Queue (RDPQ) Array support" From: Benjamin Herrenschmidt To: Sreekanth Reddy Cc: "Martin K. Petersen" , James Bottomley , Linux Kernel Mailing List , scsi , Christoph Hellwig Date: Fri, 20 Feb 2015 16:01:40 +1100 Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.7-0ubuntu1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Sreekanth ! While looking at some (unrelated) issue where mtp2sas seems to be using 32-bit DMA instead of 64-bit DMA on some POWER platforms, I noticed this patch which was merged as 5fb1bf8aaa832e1e9ca3198de7bbecb8eff7db9c. Can you confirm my understanding that you are: - Setting the DMA mask to 32-bit - Mapping pages for DMA - Changing the DMA mask to 64-bit ? If yes, then I don't think this is a legal thing to do and definitely not something supported by all architectures. It might work by accident, but there is no telling that any translation/DMA mapping provided before a call to set_dma_mask() is still valid after that call. The architecture might have to completely reconfigure the iommu, for example on some PowerPC platforms, we switch from a remapped mapping to a direct linear map of all memory, all translations established before the switch might be lost (it depends on the specific implementation). How does it work on x86 with DMAR ? Cheers, Ben.