From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752060AbaIWFN5 (ORCPT ); Tue, 23 Sep 2014 01:13:57 -0400 Received: from top.free-electrons.com ([176.31.233.9]:53531 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751209AbaIWFN4 (ORCPT ); Tue, 23 Sep 2014 01:13:56 -0400 Date: Tue, 23 Sep 2014 07:13:52 +0200 From: Boris BREZILLON To: Arnd Bergmann Cc: Samuel Ortiz , Lee Jones , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mfd: inherit coherent_dma_mask from parent device Message-ID: <20140923071352.65a6e9ec@bbrezillon> In-Reply-To: <12718317.Y05azLtl8v@wuerfel> References: <1411414675-19010-1-git-send-email-boris.brezillon@free-electrons.com> <12718317.Y05azLtl8v@wuerfel> X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.23; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Arnd, On Mon, 22 Sep 2014 21:45:40 +0200 Arnd Bergmann wrote: > On Monday 22 September 2014 21:37:55 Boris BREZILLON wrote: > > dma_mask and dma_parms are already inherited from the parent device but > > dma_coherent_mask was left uninitialized (set to zero thanks to kzalloc). > > Set sub-device coherent_dma_mask to its parent value to simplify > > sub-drivers making use of dma coherent helper functions (those drivers > > currently have to explicitly set the dma coherent mask using > > dma_set_coherent_mask function). > > > > Signed-off-by: Boris BREZILLON > > --- > > > > Hi, > > > > This patch is follow-up of a discussion we had on a KMS driver thread [1]. > > This patch is only copying the parent device coherent_dma_mask to avoid > > calling specific dma_set_coherent_mask in case the coherent mask is the > > default one. > > > > I'm a bit surprised this hasn't been done earlier while other dma fields > > (mask and parms) are already inherited from the parent device, so please > > tell me if there already was an attempt to do the same, and if so, what > > was the reson for rejecting it :-). > > > > > > Seems reasonable to me. It's not clear whether we should always inherit > the dma_mask, but I see no point in copying just dma_mask but not > coherent_dma_mask. I thought about adding a dma_mask field to mfd_cell to override the default behavior (allocate a new dma_mask and copy the value provided by mfd_cell if it's not zero), but I don't see any real use case where a sub-device does not share the dma capabilities with its parent. IMHO, it's safer to keep it as is until someone really need to set a different dma_mask on a sub-device. Best Regards, Boris -- Boris Brezillon, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com