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From: Arnd Bergmann <arnd@arndb.de>
To: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Cc: linux-arm-kernel@lists.infradead.org,
        Nicolas Ferre <nicolas.ferre@atmel.com>,
        Boris Brezillon <boris.brezillon@free-electrons.com>,
        Stephen Boyd <sboyd@codeaurora.org>, linux-kernel@vger.kernel.org,
        Cyrille Pitchen <cyrille.pitchen@atmel.com>,
        Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>,
        linux-clk@vger.kernel.org
Subject: Re: [PATCH 01/48] clk: at91: replace usleep() by udelay() calls
Date: Mon, 13 Jun 2016 21:26:49 +0200
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On Monday, June 13, 2016 5:24:09 PM CEST Alexandre Belloni wrote:
> On 11/06/2016 at 00:30:36 +0200, Arnd Bergmann wrote :
> > On Saturday, June 11, 2016 12:03:04 AM CEST Alexandre Belloni wrote:
> > > From: Cyrille Pitchen <cyrille.pitchen@atmel.com>
> > > 
> > > Fix the main and slow clock .prepare() implementations which used to call
> > > usleep() when the scheduler wasn't ready yet.
> > > 
> > 
> > Does this have to be called that early? It seems wasteful to always
> > call udelay() here, when these are functions that are normally
> > allowed to sleep.
> > 
> 
> So I've tested it and something like that would work:
> 
>         if (system_state < SYSTEM_RUNNING)
>                 udelay(osc->startup_usec);
>         else
>                 usleep_range(osc->startup_usec, osc->startup_usec + 1);

I think that's reasonable in this case.

> But I'm afraid it would be the first driver to actually do something
> like that (however, it is already the only driver trying to sleep). 

We have a lot of drivers that call potentially sleeping function from
the .prepare callback, e.g. when they go to an i2c controller.

	Arnd