linux-kernel - Re: [PATCH v3 02/11] pwm: imx: remove ipg clock

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Message-ID: <1477992404.2475.40.camel@pengutronix.de>
Date:   Tue, 01 Nov 2016 10:26:44 +0100
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Lukasz Majewski <l.majewski@...ess.pl>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Stefan Agner <stefan@...er.ch>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Fabio Estevam <fabio.estevam@....com>,
        Fabio Estevam <festevam@...il.com>,
        Lothar Wassmann <LW@...o-electronics.de>,
        Bhuvanchandra DV <bhuvanchandra.dv@...adex.com>,
        kernel@...gutronix.de
Subject: Re: [PATCH v3 02/11] pwm: imx: remove ipg clock

Am Dienstag, den 01.11.2016, 08:10 +0100 schrieb Lukasz Majewski:
> From: Sascha Hauer <s.hauer@...gutronix.de>
> 
> The use of the ipg clock was introduced with commit 7b27c160c681
> ("pwm: i.MX: fix clock lookup").
> In the commit message it was claimed that the ipg clock is enabled for
> register 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.
> 
> Signed-off-by: Sascha Hauer <s.hauer@...gutronix.de>
> Cc: Philipp Zabel <p.zabel@...gutronix.de>

I don't remember the details, but since I had only worked with i.MX53
and i.MX6 at the time, and Sascha now verified that the i.MX53 PWM
registers can in fact be accessed with the pwmX_ipg_clk bits gated, I
can only assume that this patch is the result of a misinterpretation of
the i.MX53 technical reference manual: Contrary to the i.MX6 TRM it does
not mention the ungated peripheral access clock (ipg_clk_s) at all, but
calls the gated ipg_clk "block interface clock" in Table 18-3.

Acked-by: Philipp Zabel <p.zabel@...gutronix.de>

regards
Philipp