From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lars-Peter Clausen Subject: Re: [alsa-devel] [PATCH v5 06/10] dmaengine: add API for getting dma controller's quirk Date: Fri, 09 Oct 2015 13:38:05 +0200 Message-ID: <5617A71D.4030006@metafoo.de> References: <1442187923-5736-1-git-send-email-shawn.lin@rock-chips.com> <1442188139-6017-1-git-send-email-shawn.lin@rock-chips.com> <20151005153746.GG13501@vkoul-mobl.iind.intel.com> <56139289.7000005@rock-chips.com> <561629D6.9010702@metafoo.de> <5617A589.4090102@rock-chips.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Addy Ke , Heiko Stuebner , alsa-devel@alsa-project.org, linux-rockchip@lists.infradead.org, linux-kernel@vger.kernel.org, linux-spi@vger.kernel.org, Doug Anderson , Takashi Iwai , dmaengine@vger.kernel.org, Mark Brown , Olof Johansson , Sonny Rao , linux-arm-kernel@lists.infradead.org To: Shawn Lin , Vinod Koul Return-path: In-Reply-To: <5617A589.4090102@rock-chips.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-spi.vger.kernel.org On 10/09/2015 01:31 PM, Shawn Lin wrote: > =E5=9C=A8 2015/10/8 16:31, Lars-Peter Clausen =E5=86=99=E9=81=93: >> On 10/06/2015 11:21 AM, Shawn Lin wrote: >>> Hi Vinod, >>> >>> On 2015/10/5 23:37, Vinod Koul wrote: >>>> On Mon, Sep 14, 2015 at 07:48:59AM +0800, Shawn Lin wrote: >>>>> Add dmaengine_get_quirks API for peripheral devices to query >>>>> quirks if they need it to make special workaround due to broken >>>>> dma controller design. >>>>> >>>>> Signed-off-by: Shawn Lin >>>>> --- >>>>> >>>>> Changes in v5: None >>>>> Changes in v4: None >>>>> Changes in v3: None >>>>> Changes in v2: None >>>>> Changes in v1: None >>>>> >>>>> include/linux/dmaengine.h | 9 +++++++++ >>>>> 1 file changed, 9 insertions(+) >>>>> >>>>> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.= h >>>>> index e2f5eb4..5174ca4 100644 >>>>> --- a/include/linux/dmaengine.h >>>>> +++ b/include/linux/dmaengine.h >>>>> @@ -704,6 +704,7 @@ struct dma_device { >>>>> >>>>> int (*device_config)(struct dma_chan *chan, >>>>> struct dma_slave_config *config); >>>>> + int (*device_get_quirks)(struct dma_chan *chan); >>>> >>>> And why do we want to expose this to users? THis doesnt seem right= ! >>>> >>> >>> Basically I agree not to expose dma's quirk to slave controllers...= But, the >>> fact I mentioned on cover letter explain the reasons why I have to = let slave >>> controllers know that they are working with a broken dma. It's a di= lemma >>> that if we don't want that to be exposed(let slave controllers' dri= ver get >>> the info via a API), we have t add broken quirk for all of them ,he= re and >>> there, which seems to be a disaster:( >> >> The problem with this API is that it transports values with device s= pecific >> meanings over a generic API. Which is generally speaking not a good = idea >> because the consumer witch is supposed to be generic suddenly needs = to know >> which provider it is talking to. >> >> A better solution in this case typically is either introduce a gener= ic API >> with generic values or a custom API with custom values, but don't mi= x the >> two. >> >>> >>> I would appreciate it if you could give me some suggestions at your= earliest >>> convenience. :) >> >> In this case I think the best way to handle this is not quirks, but = rather >> expose the actual maximum burst size using the DMA capabilities API.= Since >> supporting only a certain burst depth is not really a quirk. All har= dware >> has a limit for this and for some it might be larger or smaller than= for >> others and it might be the same IP core but the maximum size depends= on some >> IP core parameters. So this should be discoverable. >> >=20 > Hi Lars, >=20 > Thanks for looking for that. >=20 > It's a good idea if all clients of the Soc are broken, but unfortunat= ely > some of them work. So... max burst shoule be different for individual= s. Well, the dma_get_slave_caps() API works on a DMA channel, so I don't t= hink this will be a problem. - Lars