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

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Date:   Mon, 25 Feb 2019 16:57:43 +0100
From:   Pierre Yves MORDRET <pierre-yves.mordret@...com>
To:     Lucas Stach <l.stach@...gutronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>
CC:     <devicetree@...r.kernel.org>,
        Philippe Cornu <philippe.cornu@...com>,
        <linux-kernel@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v1 2/3] ARM: dts: stm32: enable Vivante GPU support on
 stm32mp157c-ed1 board

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@...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@...00000 {
>> +			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>;