linux-kernel - RE: [EXT] Re: Issue: regmap: use debugfs even when no device

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Message-ID: <VI1PR0402MB3600AD425469BAF9BCC5CC2FFF1F0@VI1PR0402MB3600.eurprd04.prod.outlook.com>
Date:   Wed, 29 May 2019 01:33:46 +0000
From:   Andy Duan <fugang.duan@....com>
To:     Mark Brown <broonie@...nel.org>
CC:     "david@...hnology.com" <david@...hnology.com>,
        "rafael@...nel.org" <rafael@...nel.org>,
        Robby Cai <robby.cai@....com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: RE: [EXT] Re: Issue: regmap: use debugfs even when no device


From: Mark Brown <broonie@...nel.org> Sent: Tuesday, May 28, 2019 9:27 PM
> On Tue, May 28, 2019 at 02:20:15AM +0000, Andy Duan wrote:
> 
> > So on i.MX8MM/8QM/8QXP platforms, we catch the issue that user dump
> > regmap registers without power cause system hang.
> > Maybe revert the patch is more reasonable ?
> 
> This is an issue with or without a device - you can have the same issue with
> devices that are powered off.  Typically where power is dynamic the driver
> will use a register cache so the registers are always available.

Correct, regmap without device also has issue when power if off, because regmap
doesn't implement runtime pm for the device, but maybe device driver implement
the runtime pm for the device. 

So regmap how to manage the clock and power when access registers by debugfs ?

Andy