Re: [PATCH v1 2/3] ARM: dts: stm32: enable Vivante GPU support on stm32mp157c-ed1 board

[Pierre Yves MORDRET <pierre-yves.mordret@st.com>]

Hi Lucas,

I'm going to resend a new version on this DT. I have to move this region elsewhere.

However I didn't get your feedback about statement I did.
Would it be possible to have your feelings ?

Thanks :)

On 2/25/19 4:57 PM, Pierre Yves MORDRET wrote:
> Hi again,
> 
> On 2/15/19 5:14 PM, Lucas Stach wrote:
>> Am Freitag, den 15.02.2019, 16:58 +0100 schrieb Pierre-Yves MORDRET:
>>> Enable Vivante GPU driver for stm32mp157c-ed1 board.
>>>
>>> Signed-off-by: Pierre-Yves MORDRET <pierre-yves.mordret@st.com>
>>> ---
>>>  arch/arm/boot/dts/stm32mp157c-ed1.dts | 16 ++++++++++++++++
>>>  1 file changed, 16 insertions(+)
>>>
>>> diff --git a/arch/arm/boot/dts/stm32mp157c-ed1.dts
>>> b/arch/arm/boot/dts/stm32mp157c-ed1.dts
>>> index 98ef7a0..792f402 100644
>>> --- a/arch/arm/boot/dts/stm32mp157c-ed1.dts
>>> +++ b/arch/arm/boot/dts/stm32mp157c-ed1.dts
>>> @@ -20,6 +20,17 @@
>>>  		reg = <0xC0000000 0x40000000>;
>>>  	};
>>>  
>>> +	reserved-memory {
>>> +		#address-cells = <1>;
>>> +		#size-cells = <1>;
>>> +		ranges;
>>> +
>>> +		gpu_reserved: gpu@f8000000 {
>>> +			reg = <0xf8000000 0x8000000>;
>>> +			no-map;
>>> +		};
>>> +	};
>>> +
>>
>> I don't think you need this. The GPU driver uses very little contig dma
>> memory. Most of the GPU memory is ordinary paged memory, so setting
>> aside a private memory region of this size is a waste of memory. Most
>> likely you can just allow the GPU driver to use the system global CMA
>> region.
> 
> That's correct, but this memory area is also used for U-BOOT splash screen
> rendering.
> Moreover, even if we lack of proof as for today, it turns out performances are
> better with this region as reduces MMU accesses (with Vivante driver)
> Eventually using Android framework application is started more gently whatever
> previous application and CMA status(fragmentation).
> Provided this memory, CMA region is decreased accordingly.
> 
> Hope it clarifies.
> 
> Regards
>>
>> Regards,
>> Lucas
>>
>>
>>>  	aliases {
>>>  		serial0 = &uart4;
>>>  	};
>>> @@ -53,6 +64,11 @@
>>>  	status = "okay";
>>>  };
>>>  
>>> +&gpu {
>>> +	contiguous-area = <&gpu_reserved>;
>>> +	status = "okay";
>>> +};
>>> +
>>>  &i2c4 {
>>>  	pinctrl-names = "default";
>>>  	pinctrl-0 = <&i2c4_pins_a>;
> 
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