From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751053Ab1ITNHq (ORCPT ); Tue, 20 Sep 2011 09:07:46 -0400 Received: from e24smtp04.br.ibm.com ([32.104.18.25]:59859 "EHLO e24smtp04.br.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750801Ab1ITNHp (ORCPT ); Tue, 20 Sep 2011 09:07:45 -0400 From: Thadeu Lima de Souza Cascardo To: benh@kernel.crashing.org Cc: linux-kernel@vger.kernel.org, nhorman@redhat.com, jesse.brandeburg@intel.com, alexander.h.duyck@intel.com, Thadeu Lima de Souza Cascardo , Paul Mackerras , linuxppc-dev@lists.ozlabs.org Subject: [PATCH] powerpc: reserve iommu page 0 Date: Tue, 20 Sep 2011 10:07:24 -0300 Message-Id: <1316524044-5260-1-git-send-email-cascardo@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.4.4 x-cbid: 11092013-8936-0000-0000-00000480A5A9 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Some devices have a dma-window that starts at the address 0. This allows DMA addresses to be mapped to this address and returned to drivers as a valid DMA address. Some drivers may not behave well in this case, since the address 0 is considered an error or not allocated. The solution to avoid this kind of error from happening is reserve the page addressed as 0 so it cannot be allocated for a DMA mapping. Ben Herrenschmidt deserves the credit for this patch. He pointed out the solution and what code would do the job. Signed-off-by: Thadeu Lima de Souza Cascardo Cc: Benjamin Herrenschmidt Cc: Paul Mackerras Cc: linuxppc-dev@lists.ozlabs.org --- arch/powerpc/kernel/iommu.c | 3 +++ 1 files changed, 3 insertions(+), 0 deletions(-) diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c index 961bb03..53411bc 100644 --- a/arch/powerpc/kernel/iommu.c +++ b/arch/powerpc/kernel/iommu.c @@ -501,6 +501,9 @@ struct iommu_table *iommu_init_table(struct iommu_table *tbl, int nid) tbl->it_map = page_address(page); memset(tbl->it_map, 0, sz); + if (tbl->it_offset == 0) + set_bit(0, tbl->it_map); + tbl->it_hint = 0; tbl->it_largehint = tbl->it_halfpoint; spin_lock_init(&tbl->it_lock); -- 1.7.4.4