linux-kernel - Re: [linux-sunxi] Re: [PATCH 7/8] arm64: dts: allwinner: Add Allwinner H616 .dtsi file

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Date:   Thu, 3 Dec 2020 23:02:31 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     André Przywara <andre.przywara@....com>
Cc:     Samuel Holland <samuel@...lland.org>,
        Maxime Ripard <mripard@...nel.org>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        devicetree <devicetree@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        Rob Herring <robh+dt@...nel.org>,
        Icenowy Zheng <icenowy@...c.xyz>,
        Yangtao Li <frank@...winnertech.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [linux-sunxi] Re: [PATCH 7/8] arm64: dts: allwinner: Add
 Allwinner H616 .dtsi file

On Thu, Dec 3, 2020 at 6:54 PM André Przywara <andre.przywara@....com> wrote:
>
> On 03/12/2020 03:16, Samuel Holland wrote:
>
> Hi,
>
> > On 12/2/20 7:54 AM, Andre Przywara wrote:
> > ...
> >> +    soc {
> >> +            compatible = "simple-bus";
> >> +            #address-cells = <1>;
> >> +            #size-cells = <1>;
> >> +            ranges = <0x0 0x0 0x0 0x40000000>;
> >> +
> >> +            syscon: syscon@...0000 {
> >> +                    compatible = "allwinner,sun50i-h616-system-control",
> >> +                                 "allwinner,sun50i-a64-system-control";
> >> +                    reg = <0x03000000 0x1000>;
> >> +                    #address-cells = <1>;
> >> +                    #size-cells = <1>;
> >> +                    ranges;
> >> +
> >> +                    sram_c: sram@...00 {
> >> +                            compatible = "mmio-sram";
> >> +                            reg = <0x00028000 0x30000>;
> >> +                            #address-cells = <1>;
> >> +                            #size-cells = <1>;
> >> +                            ranges = <0 0x00028000 0x30000>;
> >> +                    };
> >> +
> >> +                    sram_c1: sram@...0000 {
> >> +                            compatible = "mmio-sram";
> >> +                            reg = <0x01a00000 0x200000>;
> >> +                            #address-cells = <1>;
> >> +                            #size-cells = <1>;
> >> +                            ranges = <0 0x01a00000 0x200000>;
> >> +
> >> +                            ve_sram: sram-section@0 {
> >> +                                    compatible = "allwinner,sun50i-h616-sram-c1",
> >> +                                                 "allwinner,sun4i-a10-sram-c1";
> >> +                                    reg = <0x000000 0x200000>;
> >> +                            };
> >> +                    };
> >> +            };
> >
> > You mentioned that you could not find a SRAM A2. How were these SRAM ranges
> > verified? If you can load eGON.BT0 larger than 32 KiB, then presumably NBROM
> > uses SRAM C, and it is in the manual, but I see no mention of SRAM C1.
>
> The manual says that SRAM C *can* be used by "the system", at boot time,
> as long as it's configured correctly. I couldn't find any details on how
> to switch clock sources for SRAM C, and the manual stanza on this is
> quite gibberish. I presume it's configured either by BROM or by reset
> default this way. I think the idea is that the later users (VE, DE) take
> ownership at some point (which means we can't run any firmware in there).
> The BSP boot0 is 48KB already, so reaching into SRAM C, and the code
> itself heavily uses SRAM C (found by hacking boot0 to drop to FEL and
> inspecting the memory afterwards).
>
> For C1: I copied this name from the H6 .dtsi, the manual calls this
> "VE-SRAM", in both manuals, and the description looks identical there
> for both SoCs. I think this will be later used by the video engine, so I
> kept it in. The large size made me suspicious, and from former
> experiments it looks like being aliased to (parts of) SRAM C.

I would just call it sram_ve or ve_sram. SRAM C1 would make more sense if
it were part of SRAM C, not the other way around.

Also the sram-section node would make more sense if it were in sram_c, as
that is the part that gets switched around, not the full region @ 1a00000.

ChenYu

> Maybe some guys with more VE knowledge can shine some light on this?
>
> Cheers,
> Andre
>
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