linux-kernel - Re: [PATCH] fbdev: simplefb: add support for 'memory-region' property on DT node

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Message-Id: <20180202142121.CEB8.4A936039@socionext.com>
Date:   Fri, 02 Feb 2018 14:21:21 +0900
From:   Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Hans de Goede <hdegoede@...hat.com>,
        linux-fbdev@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        devicetree <devicetree@...r.kernel.org>
Subject: Re: [PATCH] fbdev: simplefb: add support for 'memory-region' property on DT node

Hi Andy,

On Thu, 1 Feb 2018 21:03:30 +0200 <andy.shevchenko@...il.com> wrote:

> On Thu, Feb 1, 2018 at 5:56 PM, Bartlomiej Zolnierkiewicz
> <b.zolnierkie@...sung.com> wrote:
> > On Tuesday, January 23, 2018 08:34:56 PM Kunihiko Hayashi wrote:
> >> Enables 'memory-region' property referring to the memory description on
> >> the reserved-memory node in case of devicetree use.
> >> If there is no 'reg' property that specifies the address and size of
> >> the framebuffer, the address and size written in the memory description
> >> on the reserved-memory node can be used for the framebuffer.
> >>
> >> Furthermore, the reserved-memory node needs to have "no-map" attributes
> >> because simplefb driver maps the region by ioremap_wc().
> >>
> >> Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
> 
> >> +- memory-region: phandle to a node describing memory region as framebuffer
> >> +              memory instead of reg property. The node should include
> >> +              'no-map'.
> 
> >>       mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> >> +     if (!mem)
> >> +             mem = simplefb_parse_dt_reserved_mem(&pdev->dev);
> 
> I'm not sure I understood why you need this entire function?
> 
> Put your memory resource ('reg' property) as part of reserved memory
> with necessary flags.

Surely we prepare a memory resource as a part of reserved memory,
for example:

	reserved-memory {
		fb_area: memory@...0000000 {
			reg = <0xa0000000 0x400000>;
			no-map;
		};
	};

And we need to specify the address and size as a reg property in
the framebuffer node.

	framebuffer {
		compatible = "simple-framebuffer";
		reg = <0xa0000000 0x400000>;
	};

This function allows us to specify the area with phandle to
the reserved memory instead of same address and size.

	framebuffer {
		compatible = "simple-framebuffer";
		memory-region = <&fb_area>;
	};

If both reg and memory-region properties are specified
in the framebuffer node, the reg propery will be applied.

---
Best Regards,
Kunihiko Hayashi