linux-kernel - RE: DRM Driver implementation question

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Date:   Tue, 17 Sep 2019 04:38:58 +0000
From:   Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
To:     Gareth Williams <gareth.williams.jx@...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 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