From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jon Hunter Subject: Re: [PATCH v3 09/13] dmaengine: tegra-apb: Remove runtime PM usage Date: Tue, 7 Jan 2020 18:38:36 +0000 Message-ID: <01660250-0489-870a-6f0e-d74c5041e8e3@nvidia.com> References: <20200106011708.7463-1-digetx@gmail.com> <20200106011708.7463-10-digetx@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Dmitry Osipenko , Laxman Dewangan , Vinod Koul , Dan Williams , Thierry Reding , =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= Cc: dmaengine@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-tegra@vger.kernel.org On 07/01/2020 17:12, Dmitry Osipenko wrote: > 07.01.2020 18:13, Jon Hunter =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >> >> On 06/01/2020 01:17, Dmitry Osipenko wrote: >>> There is no benefit from runtime PM usage for the APB DMA driver becaus= e >>> it enables clock at the time of channel's allocation and thus clock sta= ys >>> enabled all the time in practice, secondly there is benefit from manual= ly >>> disabled clock because hardware auto-gates it during idle by itself. >> >> This assumes that the channel is allocated during a driver >> initialisation. That may not always be the case. I believe audio is one >> case where channels are requested at the start of audio playback. >=20 > At least serial, I2C, SPI and T20 FUSE are permanently keeping channels > allocated, thus audio is an exception here. I don't think that it's > practical to assume that there is a real-world use-case where audio > driver is the only active DMA client. >=20 > The benefits of gating the DMA clock are also dim, do you have any > power-consumption numbers that show that it's really worth to care about > the clock-gating? No, but at the same time, I really don't see the point in this. In fact, I think it is a step backwards. If we wanted to only enable clocks while DMA channels are active we could. So I request you drop this. Jon --=20 nvpublic