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Subject: Re: [linux-sunxi] Re: [PATCH 7/8] arm64: dts: allwinner: Add
 Allwinner H616 .dtsi file
To:     Chen-Yu Tsai <wens@csie.org>
Cc:     Samuel Holland <samuel@sholland.org>,
        Maxime Ripard <mripard@kernel.org>,
        Jernej Skrabec <jernej.skrabec@siol.net>,
        devicetree <devicetree@vger.kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-sunxi <linux-sunxi@googlegroups.com>,
        Rob Herring <robh+dt@kernel.org>,
        Icenowy Zheng <icenowy@aosc.xyz>,
        Yangtao Li <frank@allwinnertech.com>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
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Organization: ARM Ltd.
Message-ID: <3dc67c21-f649-cca5-ec54-c639c54ee56a@arm.com>
Date:   Thu, 3 Dec 2020 15:44:58 +0000
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On 03/12/2020 15:02, Chen-Yu Tsai wrote:
> On Thu, Dec 3, 2020 at 6:54 PM André Przywara <andre.przywara@arm.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@3000000 {
>>>> +                    compatible = "allwinner,sun50i-h616-system-control",
>>>> +                                 "allwinner,sun50i-a64-system-control";
>>>> +                    reg = <0x03000000 0x1000>;
>>>> +                    #address-cells = <1>;
>>>> +                    #size-cells = <1>;
>>>> +                    ranges;
>>>> +
>>>> +                    sram_c: sram@28000 {
>>>> +                            compatible = "mmio-sram";
>>>> +                            reg = <0x00028000 0x30000>;
>>>> +                            #address-cells = <1>;
>>>> +                            #size-cells = <1>;
>>>> +                            ranges = <0 0x00028000 0x30000>;
>>>> +                    };
>>>> +
>>>> +                    sram_c1: sram@1a00000 {
>>>> +                            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.

But isn't that what we do? "sram_c1" is just the node name alias used
for the parent node. That is actually never referenced anywhere (in any
of the the H6 .dts), so we can actually remove it, I guess.
The actual SRAM section is called ve_sram already.
And I can't change the compatible name, for the fallback, at least.

I can make the new compatible string read
"allwinner,sun50i-h616-ve-sram", if that helps, but that would mean
deviating from the H6 and other SoCs.

Cheers,
Andre


> 
> 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
>>