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

[Dmitry Osipenko]

On 28.09.2017 17:06, Dmitry Osipenko wrote:
> 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.
> 

Also, shouldn't prep_ and dma_slave_config be protected with locking? I don't
see DMA core doing any locking and seems none of the drivers too.

-- 
Dmitry