linux-kernel - Re: Allocation of frame buffer at a specific memory range or address

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Date:	Sat, 16 Apr 2016 17:48:04 -0400
From:	Rob Clark <robdclark@...il.com>
To:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
Cc:	Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"daniel@...ll.ch" <daniel@...ll.ch>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-snps-arc@...ts.infradead.org" 
	<linux-snps-arc@...ts.infradead.org>,
	"airlied@...ux.ie" <airlied@...ux.ie>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Rob Herring <robh@...nel.org>
Subject: Re: Allocation of frame buffer at a specific memory range or address

On Sat, Apr 16, 2016 at 2:07 AM, Vineet Gupta
<Vineet.Gupta1@...opsys.com> wrote:
> On Friday 15 April 2016 09:18 PM, Alexey Brodkin wrote:
>
>> And now the question is how to force DRM subsystem or just that driver
>> to use whatever predefined (say via device tree) location in memory
>> for data buffer allocation.
>
> It seems this is pretty easy to do with DT reserved-memory binding.
>
> You need to partition memory into @memory and @reserved-memory.
> Later can be subdivided into more granular regions and your driver can refer to
> one of the regions.

jfyi, it might be useful to look at msm_init_vram() which has support
to wrap vram carveout as gem buffer, for exact same purpose..

BR,
-R


> Something like below (untested)
>
> +       memory {
> +               device_type = "memory";
> +               reg = <0x0 0x80000000 0x0 0xA0000000>;
> +               #address-cells = <2>;
> +               #size-cells = <2>;
> +       };
> +
> +       reserved-memory {
> +               #address-cells = <2>;
> +               #size-cells = <2>;
> +               ranges;
> +               /* This memory bypasses IOC port */
> +               fb_reserved@...00000 {
> +                       reg = <0x0 0xA0000000 0x0 0xAF000000>;
> +                       #address-cells = <2>;
> +                       #size-cells = <2>;
> +                       /* no-map;   */
> +               };
> +       };
> +
> +
> +       fb0: video@...00000 {
> +               memory-region = <&fb_reserved>;
> +               /* ... */
> +       };
>
> This might also need a DT helper in ARC mm init code.
>
> +       early_init_fdt_scan_reserved_mem();
>
> HTH,
> -Vineet