Re: [PATCH v1 4/5] dmaengine: Add driver for NVIDIA Tegra AHB DMA controller

[Dmitry Osipenko]

On 28.09.2017 12:29, Vinod Koul wrote:
>> +	default:
>> +		return -EINVAL;
>> +	}
>> +
>> +	ahb_seq  = burst << TEGRA_AHBDMA_CHANNEL_AHB_BURST_SHIFT;
>> +	ahb_seq |= TEGRA_AHBDMA_CHANNEL_ADDR_WRAP;
>> +	ahb_seq |= TEGRA_AHBDMA_CHANNEL_INTR_ENB;
>> +
>> +	writel_relaxed(ahb_seq,
>> +		       ahbdma_chan->regs + TEGRA_AHBDMA_CHANNEL_AHB_SEQ);
>> +
>> +	writel_relaxed(ahb_addr,
>> +		       ahbdma_chan->regs + TEGRA_AHBDMA_CHANNEL_AHB_PTR);
> 
> oh no, you don't write to HW here. This can be called anytime when you have
> txn running! You should save these and use them in prep_ calls.
> 

BTW, some of the DMA drivers have exactly the same problem. I now see that it is
actually documented explicitly in provider.txt, but that's inconsistent across
the actual drivers.

-- 
Dmitry