linux-kernel - Re: [PATCH v17 2/4] dmaengine: tegra: Add tegra gpcdma driver

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Message-ID: <08f6571e-af75-b6b3-443e-e86e3bdb365b@gmail.com>
Date:   Mon, 31 Jan 2022 02:11:41 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Akhil R <akhilrajeev@...dia.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Krishna Yarlagadda <kyarlagadda@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        Rajesh Gumasta <rgumasta@...dia.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "vkoul@...nel.org" <vkoul@...nel.org>
Cc:     Pavan Kunapuli <pkunapuli@...dia.com>
Subject: Re: [PATCH v17 2/4] dmaengine: tegra: Add tegra gpcdma driver

30.01.2022 19:34, Akhil R пишет:
>> 29.01.2022 19:40, Akhil R пишет:
>>> +static int tegra_dma_device_pause(struct dma_chan *dc) {
>>> +     struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
>>> +     unsigned long wcount, flags;
>>> +     int ret = 0;
>>> +
>>> +     if (!tdc->tdma->chip_data->hw_support_pause)
>>> +             return 0;
>>
>> It's wrong to return zero if pause unsupported, please see what
>> dmaengine_pause() returns.
>>
>>> +
>>> +     spin_lock_irqsave(&tdc->vc.lock, flags);
>>> +     if (!tdc->dma_desc)
>>> +             goto out;
>>> +
>>> +     ret = tegra_dma_pause(tdc);
>>> +     if (ret) {
>>> +             dev_err(tdc2dev(tdc), "DMA pause timed out\n");
>>> +             goto out;
>>> +     }
>>> +
>>> +     wcount = tdc_read(tdc, TEGRA_GPCDMA_CHAN_XFER_COUNT);
>>> +     tdc->dma_desc->bytes_xfer +=
>>> +                     tdc->dma_desc->bytes_req - (wcount * 4);
>>
>> Why transfer is accumulated?
>>
>> Why do you need to update xfer size at all on pause?
> 
> I will verify the calculation. This looks correct only for single sg transaction.
> 
> Updating xfer_size is added to support drivers which pause the transaction
> and read the status before terminating. 
> Eg. https://elixir.bootlin.com/linux/latest/source/drivers/tty/serial/amba-pl011.c

Why you couldn't update the status in tegra_dma_terminate_all()?