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From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Thierry Reding <thierry.reding@gmail.com>
Cc: Ryder Lee <ryder.lee@mediatek.com>,
	Rob Herring <robh+dt@kernel.org>,
	linux-pwm@vger.kernel.org, Weijie Gao <weijie.gao@mediatek.com>,
	Roy Luo <cheng-hao.luo@mediatek.com>,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-mediatek@lists.infradead.org,
	John Crispin <john@phrozen.org>
Subject: Re: [resend PATCH 1/3] pwm: mediatek: drop flag 'has_clks'
Date: Fri, 16 Nov 2018 07:47:48 +0100	[thread overview]
Message-ID: <20181116064748.6c7shn3am4wejrnj@pengutronix.de> (raw)
In-Reply-To: <20181114124752.GI2620@ulmo>

On Wed, Nov 14, 2018 at 01:47:52PM +0100, Thierry Reding wrote:
> On Tue, Nov 13, 2018 at 10:08:22AM +0800, Ryder Lee wrote:
> > The flag 'has_clks' and related checks are superfluous as the CCF
> > subsystem does this for you.
> 
> Both of these mechanisms aren't equivalent. While CCF can deal with
> optional clocks, what the has_clks flag actually means is that the
> device doesn't need a clock (or doesn't have a clock input) on the
> devices where it is cleared.
> 
> So I'd actually be in favor of keeping the has_clks property because it
> serves as an additional sanity check. For example if you run this driver
> on an SoC that "has clocks" but if you don't list them in DT, then after
> this patch the driver will happily continue without clocks, even though
> it may break completely without those clocks. I've seen SoCs respond to
> disabled clocks for a hardware block in different ways, in many cases an
> access to any of the registers will completely hang the CPU. In other
> cases it may just crash in some other way or give you some sort of
> machine exception. None of those are good, and make the tiny bit of
> additional code required to support the has_clks flag very attractive.
> 
> But that's just my opinion. If you prefer to throw away that safety
> barrier, be my guest. But if you do, please move this functionality into
> the clock framework first and then make the driver use it.

The usual policy is: If the things specified in the dt are
wrong or incomplete, it's ok to fail however you like. So from a
correctness POV I think the change is fine.

I don't know about the mips details that John pointed out in a followup
to this mail though.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

  parent reply	other threads:[~2018-11-16  6:48 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-13  2:08 Ryder Lee
2018-11-13  2:08 ` [resend PATCH 2/3] pwm: mediatek: add pwm support for MT7629 SoC Ryder Lee
2018-11-15 19:20   ` Sean Wang
2018-11-13  2:08 ` [resend PATCH 3/3] dt-bindings: pwm: update bindings " Ryder Lee
2018-11-13  9:55   ` Uwe Kleine-König
2018-11-13  9:52 ` [resend PATCH 1/3] pwm: mediatek: drop flag 'has_clks' Uwe Kleine-König
2018-11-13 18:00   ` Stephen Boyd
2018-11-14 12:47 ` Thierry Reding
2018-11-14 13:27   ` John Crispin
2018-11-15  2:16     ` Ryder Lee
2018-11-16  6:47   ` Uwe Kleine-König [this message]
2018-11-16 10:22     ` Thierry Reding

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