linux-kernel - Re: [PATCH] dmaengine: apple-admac: Avoid accessing registers in probe

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Message-ID: <CAMT+MTTFkVcZHoC77BAVc+R_rvDfhoSQZujic9SCCqb8OkgSew@mail.gmail.com>
Date: Mon, 2 Dec 2024 17:36:28 +0100
From: Sasha Finkelstein <fnkl.kernel@...il.com>
To: Vinod Koul <vkoul@...nel.org>
Cc: Hector Martin <marcan@...can.st>, Sven Peter <sven@...npeter.dev>, 
	Alyssa Rosenzweig <alyssa@...enzweig.io>, Martin Povišer <povik+lin@...ebit.org>, 
	asahi@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dmaengine: apple-admac: Avoid accessing registers in probe

On Mon, 2 Dec 2024 at 17:27, Vinod Koul <vkoul@...nel.org> wrote:
> So looking at the driver, there is code to turn power, so what ensures
> that power is up while we are in alloc callback

There are two devices that use admacs, mca, and aop, with aop
only having a downstream driver for now. Aop's admac is controlled
by aop firmware, which does the power switching. Naturally, that firmware
has it's own idea of how power is supposed to be managed, so we can't
sequence it in such a way that the relevant admac has power when we
are running probe().