[Openpvrsgx-devgroup] A little SGX experiment with jz4780 / CI20

H. Nikolaus Schaller hns at goldelico.com
Sat Nov 2 16:42:58 CET 2019


Hi Paul,

> Am 02.11.2019 um 13:29 schrieb Paul Boddie <paul at boddie.org.uk>:
> 
> On Saturday 2. November 2019 07.39.08 H.  Nikolaus Schaller wrote:
>> 
>> I have located the jz4780 programming manual
>> but it doesn't say anything about the address
>> range where the SGX is mapped to. And maybe we
>> need to define an interrupt like for omap [1].
> 
> The programming manual isn't helpful about the PowerVR features, merely being 
> a description of the capabilities. It is a similar story with regard to the 
> Synopsys HDMI peripheral which might not even be mentioned beyond a single 
> specification entry.
> 
>> It may be possible to analyse the older 3.x
>> kernels which include a working SGX driver and
>> run on the CI20.
> 
> Fortunately, the 3.18 kernel code, specifically in drivers/gpu/drm/jz4780 
> contains files related to HDMI and the LCD peripheral. Meanwhile, the SGX 
> stuff appears in the jz4780.dtsi file from 3.18 as follows:
> 
>        gpu: jz4780-sgx at 13040000 {
>                compatible = "ingenic,jz4780-sgx";
>                reg = <0x13040000 0x4000>;
> 
>                clocks = <&cgu JZ4780_CLK_GPU>;
>                clock-names = "gpu";
> 
>                interrupt-parent = <&intc>;
>                interrupts = <63>;

Cool! I will simply copy that and give it a try...

> 
>> Or it could be possible to scan "interesting"
>> address ranges for what we would expect to be
>> an SGX register block (as we can see by
>> devmem2 on omap).
> 
> The above should give us something to go on.
> 
>> Looking into upstream code shows that GPU clocks
>> are handled by CGU code:
>> 
>> https://elixir.bootlin.com/linux/latest/source/drivers/clk/ingenic/jz4780-cgu.c#L444
> 
> Yes, I think they should be available for device tree configuration.

Looks as if that would simply provide the

               clocks = <&cgu JZ4780_CLK_GPU>;

in device tree.

> 
>> But a bigger problem to develop for the CI20
>> is that it appears there is no HDMI/LCD driver
>> in mainline kernels... So before having some
>> fix for that, we can't even expect to visualize
>> any 3D rendering.
> 
> I would have thought that the DRM driver mentioned above is at least a 
> reasonable start. I don't recall seeing the usual Ingenic LCD driver in the 
> drivers/drm directory, so it seems like an effort was made for upstreaming but 
> that it didn't happen due to the usual inertia and social factors involved. 
> And the HDMI stuff is based on work for the i.MX6 family, so I imagine that 
> this may have been mainlined at some point.

Ok, that is something to work on...

> 
>> And the latest user-space blobs for the jz4780 are
>> difficult to locate or have gone with some
>> server-shutdown:
>> 
>> 	https://elinux.org/CI20-SGX_kernel_module
>> 
>> But it seems as if there is an archived copy through
>> guest FTP at
>> 
>> 	ftp://ftp.radix.pro/3pp/Imagination/ci20/
>> 
>> It also appears that it is a slightly different
>> release than we have for OMAP:
>> 
>> 	1.14.3759903 vs. 1.14.3699939.
>> 
>> No idea if that will be a problem (maybe yes,
>> because the pvrsrcvtl seems to compare this
>> version code to make sure that the uKernel
>> does match).
> 
> I did download various user space archives for the CI20, so I can check what I 
> actually have.

If you find a 1.14.3699939 for the CI20 it would be great. If not, the
link suggested by Merlijn also works for a 1.14.3759903.

Since we also have the kernel driver source code available, we can compare
if and where they really differ and add some quirks to our driver code.

BR,
Nikolaus



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