linux-kernel - Re: [PATCH v1 2/3] clk: tegra: ignore unused vfir clock shared with uartb

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Message-ID: <20181128092404.GF17419@ulmo>
Date:   Wed, 28 Nov 2018 10:24:04 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Peter De Schrijver <pdeschrijver@...dia.com>
Cc:     Marcel Ziswiler <marcel@...wiler.com>, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Marcel Ziswiler <marcel.ziswiler@...adex.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Prashant Gaikwad <pgaikwad@...dia.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Michael Turquette <mturquette@...libre.com>,
        linux-clk@...r.kernel.org
Subject: Re: [PATCH v1 2/3] clk: tegra: ignore unused vfir clock shared with
 uartb

On Thu, Nov 01, 2018 at 10:41:52AM +0200, Peter De Schrijver wrote:
> On Thu, Nov 01, 2018 at 02:52:29AM +0100, Marcel Ziswiler wrote:
> > From: Marcel Ziswiler <marcel.ziswiler@...adex.com>
> > 
> > As UARTB and VFIR share their clock enable bit it is rather unwise for
> > the kernel to turn off the VFIR one should that be unused (and
> > potentially vice versa but so far there anyway is no VFIR driver).
> > 
> > Without this patch trying to use UARTB with the regular 8250 driver
> > will freeze as soon as ttyS1 is accessed after boot. Luckily, using the
> > high-speed Tegra serial driver won't exhibit the issue as clocks are
> > dynamically enabled/disabled on every access.
> > 
> > This has been reproduced both on Apalis T30 as well as Apalis TK1 but
> > may be an issue on all Tegra UARTB's which share the clock enable with
> > VFIR.
> > 
> 
> Ah.. the correct fix for this is to initialize the enable_refcnt based on the
> hw state. This is done in 9619dba8325fce098bbc9ee2911d1b0150fec0c9 for
> periph gate clocks, but obviously also applies to normal periph clocks.

Hi Marcel,

were you going to send a new version with the alternative fix as
suggested by Peter?

Thierry

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