linux-kernel - Re: [PATCH] clk: imx: lpcg: write twice when writing lpcg regs

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Message-ID: <20190913034213.GH17142@dragon>
Date:   Fri, 13 Sep 2019 11:42:14 +0800
From:   Shawn Guo <shawnguo@...nel.org>
To:     Anson Huang <anson.huang@....com>
Cc:     Dong Aisheng <dongas86@...il.com>, Stephen Boyd <sboyd@...nel.org>,
        Peng Fan <peng.fan@....com>,
        "festevam@...il.com" <festevam@...il.com>,
        "mturquette@...libre.com" <mturquette@...libre.com>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        Aisheng Dong <aisheng.dong@....com>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        dl-linux-imx <linux-imx@....com>, Jacky Bai <ping.bai@....com>,
        Abel Vesa <abel.vesa@....com>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] clk: imx: lpcg: write twice when writing lpcg regs

On Tue, Sep 10, 2019 at 02:47:59AM +0000, Anson Huang wrote:
> 
> 
> > On Sat, Sep 7, 2019 at 9:47 PM Stephen Boyd <sboyd@...nel.org> wrote:
> > >
> > > Quoting Peng Fan (2019-08-27 01:17:50)
> > > > From: Peng Fan <peng.fan@....com>
> > > >
> > > > There is hardware issue that:
> > > > The output clock the LPCG cell will not turn back on as expected,
> > > > even though a read of the IPG registers in the LPCG indicates that
> > > > the clock should be enabled.
> > > >
> > > > The software workaround is to write twice to enable the LPCG clock
> > > > output.
> > > >
> > > > Signed-off-by: Peng Fan <peng.fan@....com>
> > >
> > > Does this need a Fixes tag?
> > 
> > Not sure as it's not code logic issue but a hardware bug.
> > And 4.19 LTS still have not this driver support.
> 
> Looks like there is an errata for this issue, and Ranjani just sent a patch for review internally,

Having errata number in both commit log and code comment is generally
helpful.

Shawn