linux-kernel - Re: [PATCH 2/6] ARM: DTS: da850: Use the new DT bindings for the eDMA3

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Date:	Tue, 15 Dec 2015 13:44:28 +0200
From:	Peter Ujfalusi <peter.ujfalusi@...com>
To:	Sekhar Nori <nsekhar@...com>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<khilman@...prootsystems.com>
Subject: Re: [PATCH 2/6] ARM: DTS: da850: Use the new DT bindings for the
 eDMA3

On 12/15/2015 11:38 AM, Sekhar Nori wrote:
> Hi Peter,
> 
> On Friday 04 December 2015 07:23 PM, Peter Ujfalusi wrote:
>> Switch to use the ti,edma3-tpcc and ti,edma3-tptc binding for the eDMA3.
>> With the new bindings boards can customize and tweak the DMA channel
>> priority to match their needs. With the new binding the memcpy is safe
>> to be used since with the old binding it was not possible for a driver
>> to know which channel is allowed to be used as non HW triggered channel.
>> Using the new binding will allow us to reserve PaRAM slots to be used by
>> the DSP which was not possible before and prevented the da850 boards to be
>> moved to DT only.
>>
>> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
>> ---
>>  arch/arm/boot/dts/da850-enbw-cmc.dts |  5 +++++
>>  arch/arm/boot/dts/da850-evm.dts      |  5 +++++
>>  arch/arm/boot/dts/da850.dtsi         | 27 ++++++++++++++++++++++-----
>>  3 files changed, 32 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/arm/boot/dts/da850-enbw-cmc.dts b/arch/arm/boot/dts/da850-enbw-cmc.dts
>> index e750ab9086d5..ca9117624cf9 100644
>> --- a/arch/arm/boot/dts/da850-enbw-cmc.dts
>> +++ b/arch/arm/boot/dts/da850-enbw-cmc.dts
>> @@ -28,3 +28,8 @@
>>  		};
>>  	};
>>  };
>> +
>> +&edma0 {
>> +	ti,edma-reserved-slot-ranges = /bits/ 16 <32 50>;
>> +	ti,edma-memcpy-channels = /bits/ 16 <20 21>;
>> +};
>> diff --git a/arch/arm/boot/dts/da850-evm.dts b/arch/arm/boot/dts/da850-evm.dts
>> index d807285a61cd..33467feb272a 100644
>> --- a/arch/arm/boot/dts/da850-evm.dts
>> +++ b/arch/arm/boot/dts/da850-evm.dts
>> @@ -243,3 +243,8 @@
>>  	tx-num-evt = <32>;
>>  	rx-num-evt = <32>;
>>  };
>> +
>> +&edma0 {
>> +	ti,edma-reserved-slot-ranges = /bits/ 16 <32 50>;
>> +	ti,edma-memcpy-channels = /bits/ 16 <20 21>;
> 
> These correspond to PRU events. It is true that most likely they will
> never be used for peripheral DMA and can be dedicated as memcpy
> channels. However, since this is being encoded in DT, we need to be sure
> that they will never be used for peripheral DMA on this board.
> 
> So, I would prefer if you do not reserve any channels for memcpy until
> there is a real need/usecase for them. I know the board file has these
> reserved but board file could be updated as you liked. With DT we need
> to maintain backward compatibility. So I would rather do it when there
> is an actual need for it.

If we do not reserve channels for memcpy then you will have no support for
memcpy on these boards. Not sure if we use memcpy in any of our drivers in
daVinci, so it might be just fine to not have DMA memcpy support at all.
But how about using edma1's reserved channels as memcpy (19-23, 30-31)? I
don't know which channels the DSP would use on these boards, so it is never
going to be safe from that point.

> In future, if/when we gain QDMA support, the QDMA channels could be used
> for memcopy.

Well, in short there is no way to get the qDMA working in a different way
either. qDMA channel is in essence using 'normal' eDMA channel. This means
that we still need to reserve the eDMA channel to be used for memcpy, but
instead of SW triggering it (as we do it right now), we would need to use the
channel as qDMA and set things up accordingly. I don't really see the benefit
for qDMA mode to be honest.
> 
>> +};
>> diff --git a/arch/arm/boot/dts/da850.dtsi b/arch/arm/boot/dts/da850.dtsi
>> index e73f5efb3aa3..9e46eb51a8da 100644
>> --- a/arch/arm/boot/dts/da850.dtsi
>> +++ b/arch/arm/boot/dts/da850.dtsi
>> @@ -151,11 +151,28 @@
>>  
>>  		};
>>  		edma0: edma@...00000 {
>> -			compatible = "ti,edma3";
>> +			compatible = "ti,edma3-tpcc";
>>  			/* eDMA3 CC0: 0x01c0 0000 - 0x01c0 7fff */
>>  			reg =	<0x0 0x8000>;
>> -			interrupts = <11 13 12>;
>> -			#dma-cells = <1>;
>> +			reg-names = "edma3_cc";
>> +			interrupts = <11 12>;
>> +			interrupt-names = "edma3_ccint", "edma3_ccerrint";
>> +			#dma-cells = <2>;
>> +
>> +			ti,tptcs = <&edma0_tptc0 7>, <&edma0_tptc1 0>;
>> +			ti,edma-memcpy-channels = /bits/ 16 <20 21>;
> 
> Same here. I would drop this.

OK, I'll drop this part.

> 
> Thanks,
> Sekhar
> 


-- 
Péter
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