linux-kernel - Re: [Patch v2 2/4] dmaengine: tegra: Add Tegra GPC DMA driver

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Message-ID: <8fa139f2-685e-9e19-df55-bc7f84ec9a4c@gmail.com>
Date:   Thu, 6 Aug 2020 17:22:45 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Rajesh Gumasta <rgumasta@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     Krishna Yarlagadda <kyarlagadda@...dia.com>,
        Pavan Kunapuli <pkunapuli@...dia.com>
Subject: Re: [Patch v2 2/4] dmaengine: tegra: Add Tegra GPC DMA driver

06.08.2020 16:56, Rajesh Gumasta пишет:
...
>>> +static const struct __maybe_unused dev_pm_ops
>> tegra_dma_dev_pm_ops = {
>>> +     SET_NOIRQ_SYSTEM_SLEEP_PM_OPS(tegra_dma_pm_suspend,
>>> +tegra_dma_pm_resume) };
>>
>> Please explain why this is needed. All DMA should be stopped (not
>> paused) on system's suspend, shouldn't it?
> I have rechecked with HW verification team and they confirmed that after suspend, csr and channel registers will get reset hence on resume we need to restore back.
> Also GPCDMA does not support power gate as a unit.

But all registers are re-programmed on starting a DMA transfer, hence
why do you need to save-restore them on suspend-resume?