From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760795AbbJ3UIL (ORCPT ); Fri, 30 Oct 2015 16:08:11 -0400 Received: from mail-oi0-f43.google.com ([209.85.218.43]:32998 "EHLO mail-oi0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760771AbbJ3UIH (ORCPT ); Fri, 30 Oct 2015 16:08:07 -0400 Subject: Re: [PATCH 1/2] dma: add Qualcomm Technologies HIDMA management driver To: Mark Rutland , Sinan Kaya References: <1446174501-8870-1-git-send-email-okaya@codeaurora.org> <20151030150025.GF31073@leverpostej> <5633B207.5030505@codeaurora.org> <20151030182537.GB30791@leverpostej> <5633BB66.3070505@codeaurora.org> <20151030190106.GC30791@leverpostej> Cc: Andy Shevchenko , dmaengine , timur@codeaurora.org, cov@codeaurora.org, jcm@redhat.com, Rob Herring , Pawel Moll , Ian Campbell , Kumar Gala , Vinod Koul , Dan Williams , devicetree , "linux-kernel@vger.kernel.org" , leif.lindholm@linaro.org From: Al Stone X-Enigmail-Draft-Status: N1110 Message-ID: <5633CE23.7060303@linaro.org> Date: Fri, 30 Oct 2015 14:08:03 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <20151030190106.GC30791@leverpostej> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/30/2015 01:01 PM, Mark Rutland wrote: > On Fri, Oct 30, 2015 at 02:48:06PM -0400, Sinan Kaya wrote: >>>>>> It was decided by >>>>>> Linaro that CSRT will not be supported for ARM64. Hrm. I personally decided we didn't have to worry about using the CSRT (specifically, let's wait until someone has a need for it), but I know of no decision to *not* support it. Please cite a source for that claim. >> See this. >> >> https://wiki.linaro.org/LEG/Engineering/Kernel/ACPI/TablePriorities > > The CSRT is listed under "Want", not "Never" or "Don't Care", so Linaro > have certainly not said that CSRT will not be supported. If anything, > they have stated that the table should be supported. "Want" means interesting, and probably useful, but no clear indication that anyone actually needs it. At one point, we thought we might use the CSRT for describing DMA, but it turns out we have not needed to. However, let's make sure we're saying the same thing: the CSRT table is properly defined in the kernel include/acpi/actbl2.h file so one can read such a table and use it if they so choose. Nothing that we have done at Linaro in the arm64 part of the kernel relies on any of the content from the CSRT, nor does it preclude someone relying on that content. So, the CSRT is defined, and is usable, but is just not being used -- by Linaro -- at present. If that needs to change, let me know; no one has asked us to use the CSRT for a DMA engine, and we have not been provided any hardware that requires it. > I suspect that the rationale for it not being "Critical" or "Must" is > that it's possible to use contemporary systems without DMA engines, but > we will need support at some point in future. Essentially correct. We (Linaro ACPI team) would be glad to work on it, if needed. We just need to know that someone wants it, and we need to have some way to test it (i.e., aka "hardware"). > I also note that there are Linaro patches adding supoprt for DBG2 [1] , > which is listed as "Never". So the page may be out of date... Sadly, it is indeed out of date, but it is on my TODO list. The DBG2 table was originally listed as "Never" only because of the licensing; this has since changed and is now usable for consoles, so it got worked on and implemented. > Leif, Al? > > [1] https://lkml.org/lkml/2015/9/8/287 > > Thanks, > Mark. > -- ciao, al ----------------------------------- Al Stone Software Engineer Linaro Enterprise Group al.stone@linaro.org -----------------------------------