From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <digetx@gmail.com>
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Subject: Re: [PATCH v1 4/5] dmaengine: Add driver for NVIDIA Tegra AHB DMA
 controller
To: Vinod Koul <vinod.koul@intel.com>
Cc: Thierry Reding <thierry.reding@gmail.com>,
 Jonathan Hunter <jonathanh@nvidia.com>,
 Laxman Dewangan <ldewangan@nvidia.com>,
 Peter De Schrijver <pdeschrijver@nvidia.com>,
 Prashant Gaikwad <pgaikwad@nvidia.com>,
 Michael Turquette <mturquette@baylibre.com>,
 Stephen Boyd <sboyd@codeaurora.org>, Rob Herring <robh+dt@kernel.org>,
 linux-tegra@vger.kernel.org, devicetree@vger.kernel.org,
 dmaengine@vger.kernel.org, linux-clk@vger.kernel.org,
 linux-kernel@vger.kernel.org
References: <cover.1506380746.git.digetx@gmail.com>
 <0a45e058baba72124b91c663ce1d908d275f4044.1506380746.git.digetx@gmail.com>
 <20170928092949.GB30097@localhost>
From: Dmitry Osipenko <digetx@gmail.com>
Message-ID: <b601b829-d87f-99e0-dcf9-ad3f9a7195df@gmail.com>
Date: Thu, 28 Sep 2017 17:06:03 +0300
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List-ID: <linux-clk.vger.kernel.org>

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