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

["André Przywara" <andre.przywara@arm.com>]

On 03/12/2020 16:20, Chen-Yu Tsai wrote:

Hi,

> On Thu, Dec 3, 2020 at 11:45 PM André Przywara <andre.przywara@arm.com> wrote:
>>
>> 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.
> 
> This is what I had in mind:
> 
> syscon: {
>         sram_c: sram@28000 {
>                 compatible = "mmio-sram";
>                 reg = <0x00028000 0x30000>;
>                 #address-cells = <1>;
>                 #size-cells = <1>;
>                 ranges = <0 0x00028000 0x30000>;
> 
>                 /* starting address might not be correct */
>                 sram_c_ve: sram-section@0 {
>                         compatible = "allwinner,sun50i-h616-ve-sram-c",
>                                      "allwinner,sun4i-a10-sram-c1";
>                        /* 64 kiB borrowed from ve_sram */
>                         reg = <0x0 0x10000>;
>                 };
>         };
> 
>         ve_sram: sram@1a00000 {
>                 compatible = "mmio-sram";
>                 reg = <0x01a00000 0x200000>;
>                 #address-cells = <1>;
>                 #size-cells = <1>;
>         };
> };

OK, I am taking this version, but am dropping the sram_c_ve subnode,
until we know where it is, what we actually need and until we can test it.

> Another variant, trying to describe the aliasing, though it seems
> quite confusing:

I don't know the exact nature of the aliasing, only that there is some.

> 
> syscon: {
>         ve_sram: sram@1a00000 {
>                 compatible = "mmio-sram";
>                 reg = <0x01a00000 0x200000>;
>                 #address-cells = <1>;
>                 #size-cells = <1>;
>                 ranges;
> 
>                 ve_sram_c: sram-section@28000 {
>                         compatible = "allwinner,sun50i-h616-ve-sram-c",
>                                      "allwinner,sun4i-a10-sram-c1";
>                         reg = <0x28000 0x10000>;
>                 };
>         };
> };
> 
> 
> Just out of curiosity, is the whole SRAM @1a00000 accessible by the CPU?

I have no clue, but I would guess not, since I doubt that it's actually
2MB in size. I just played around a bit with it from U-Boot, and found
strings from the SPL in there.

> Does it require the system control SRAM bits to be set, or does that only
> affect the portion that SRAM C "borrows"? If it isn't accessible to the
> CPU at all, then we might as well not put it in the device tree.

Yeah, that's another option I am thinking about.

> 
>> 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.
> 
> Matching what the documents say makes more sense to me.

I will just delay this decision by not using that string in the first
place ;-)

Thanks!
Andre


> 
> Regards
> ChenYu
> 
>> 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
>>>>
>>
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