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

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Message-ID: <20170928162238.GF30097@localhost>
Date:   Thu, 28 Sep 2017 21:52:38 +0530
From:   Vinod Koul <vinod.koul@...el.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Prashant Gaikwad <pgaikwad@...dia.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Rob Herring <robh+dt@...nel.org>, linux-tegra@...r.kernel.org,
        devicetree@...r.kernel.org, dmaengine@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 4/5] dmaengine: Add driver for NVIDIA Tegra AHB DMA
 controller

On Thu, Sep 28, 2017 at 05:35:59PM +0300, Dmitry Osipenko wrote:
> 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.

In prep when you modify the list yes (with vchan I suspect that maybe taken
care), but in general yes driver needs to do that

-- 
~Vinod