linux-kernel - RE: DRM Driver implementation question

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Message-ID: <TY2PR01MB292423C617848A66F61B1027DF8F0@TY2PR01MB2924.jpnprd01.prod.outlook.com>
Date:   Tue, 17 Sep 2019 15:27:34 +0000
From:   Gareth Williams <gareth.williams.jx@...esas.com>
To:     Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
CC:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Phil Edworthy <phil.edworthy@...esas.com>,
        Fabrizio Castro <fabrizio.castro@...renesas.com>,
        "laurent.pinchart@...asonboard.com" 
        <laurent.pinchart@...asonboard.com>,
        "kieran.bingham+renesas@...asonboard.com" 
        <kieran.bingham+renesas@...asonboard.com>
Subject: RE: DRM Driver implementation question

Hi Yoshihiro,

This looks like an elegant solution that I can implement.
Many thanks for pointing me in a good direction.

> From: Yoshihiro Shimoda, Sent: Tuesday, September 17, 2019 05:39 PM
> 
> Hi Gareth,
> 
> > From: Gareth Williams, Sent: Monday, September 16, 2019 10:56 PM
> >
> > Hi Laurent/Kieran,
> >
> > I need to upstream a driver for a display controller that within its
> > registers memory region contains registers related to a PWM device. The
> PWM device is for controlling the backlight of the display.
> > Ideally, I would like to create a separated driver for the PWM, so
> > that I can re-use "pwm-backlight", but since the registers for the PWM
> > are right in the middle of the registers for the display controller I would
> need to ioremap the memory region for the PWM registers region twice,
> once from the display controller driver, and once from the PWM driver.
> > Do you think that the double ioremap would be acceptable upstream?
> 
> I think that an MFD driver can support such hardware. I checked
> Documentation/devicetree/bindings/mfd roughly, and then atmel-hlcdc.txt
> seems to have a display controller and a PWM device.
> 
> Best regards,
> Yoshihiro Shimoda

Best Regards,

Gareth Williams