linux-kernel - Re: [PATCH v2 03/10] pwm: imx: Rewrite imx_pwm_*_v1 code to facilitate switch to atomic pwm operation

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Message-ID: <20161101085935.4fitl2u6hkt63ro6@pengutronix.de>
Date:   Tue, 1 Nov 2016 09:59:35 +0100
From:   Sascha Hauer <s.hauer@...gutronix.de>
To:     Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:     linux-pwm@...r.kernel.org,
        Bhuvanchandra DV <bhuvanchandra.dv@...adex.com>,
        Lukasz Majewski <l.majewski@...ess.pl>,
        linux-kernel@...r.kernel.org, Stefan Agner <stefan@...er.ch>,
        Thierry Reding <thierry.reding@...il.com>,
        kernel@...gutronix.de, Fabio Estevam <fabio.estevam@....com>,
        Philipp Zabel <pza@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        Lothar Wassmann <LW@...o-electronics.de>
Subject: Re: [PATCH v2 03/10] pwm: imx: Rewrite imx_pwm_*_v1 code to
 facilitate switch to atomic pwm operation

On Mon, Oct 31, 2016 at 10:29:37AM +0100, Sascha Hauer wrote:
> > accesses. This is true for the ->config() callback, but not for the
> > ->set_enable() callback. Given that the ipg clock is not consistently
> > enabled for all register accesses we can assume that either it is not
> > required at all or that the current code does not work.
> > Remove the ipg clock code for now so that it's no longer in the way of
> > refactoring the driver.
> 
> For reference:
> 
> I verified on i.MX53 and i.MX25 that the ipg clock provided to the pwm
> driver is not needed when accessing registers. I would have to verify
> that on i.MX27 aswell, but I do not have a board handy at the moment.

Also on i.MX27 disabling the PWMs ipg_clk does not disable register
accesses.

Sascha

> 
> The current assumption as discussed by Philipp and me is that the ipg
> clk is only needed when the pwm output is driven by the ipg clk
> (MX3_PWMCR[16:17] = MX3_PWMCR_CLKSRC_IPG)
> 
> Sascha
> 
> -- 
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> 

-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |