linux-kernel - Re: [PATCH 2/5] clk: lpc32xx: read-only divider can propagate rate change

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Message-ID: <1515402639.5048.82.camel@baylibre.com>
Date:   Mon, 08 Jan 2018 10:10:39 +0100
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Vladimir Zapolskiy <vz@...ia.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Michael Turquette <mturquette@...libre.com>,
        linux-clk@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org,
        Sylvain Lemieux <slemieux.tyco@...il.com>,
        Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>
Subject: Re: [PATCH 2/5] clk: lpc32xx: read-only divider can propagate rate
 change

On Sat, 2018-01-06 at 16:04 +0200, Vladimir Zapolskiy wrote:
> > I added the fix to LPC32xx because it looks like the generic divider (a lot) and
> 
> right, the relevant divider operations were copied, however the difference
> is important, unfortunately there is no simple option to get rid of regmap,
> because System Control Block registers are shared with a number of other
> device drivers.

I have the same issue ;)

> 
> > appears to support CLK_DIVIDER_READ_ONLY. If it does not, could you please kill
> > the related code ?
> 
> The driver supports CLK_DIVIDER_READ_ONLY clocks, and it should not be
> changed, but all such clocks don't have children with CLK_SET_RATE_PARENT
> property, which invalidates your fix for LPC32xx. Please let me know,
> if I missed something.

You did not miss anything. I understand your choice.
I just have different approach and usually prefer to avoid these particularity
which may catch you later on. 

At least, the fact that propagation would stop with CLK_DIVIDER_READ_ONLY on
LPC32xx, even with CLK_SET_RATE_PARENT, is now known.

Adding a comment in the code to make this explicit would be nice though.

Regards
Jerome