linux-kernel - RE: [PATCH v15 2/4] dmaengine: tegra: Add tegra gpcdma driver

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Message-ID: <BN9PR12MB52730121B2B01739DA52020EC07B9@BN9PR12MB5273.namprd12.prod.outlook.com>
Date:   Mon, 20 Dec 2021 15:23:31 +0000
From:   Akhil R <akhilrajeev@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.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 v15 2/4] dmaengine: tegra: Add tegra gpcdma driver

> 16.12.2021 20:11, Akhil R пишет:
> > +static int tegra_dma_terminate_all(struct dma_chan *dc) {
> > +     struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
> > +     unsigned long wcount = 0;
> > +     unsigned long status;
> > +     unsigned long flags;
> > +     int err;
> > +
> > +     raw_spin_lock_irqsave(&tdc->lock, flags);
> > +
> > +     if (!tdc->dma_desc) {
> > +             raw_spin_unlock_irqrestore(&tdc->lock, flags);
> > +             return 0;
> > +     }
> > +
> > +     if (!tdc->busy)
> > +             goto skip_dma_stop;
> > +
> > +     if (tdc->tdma->chip_data->hw_support_pause)
> > +             err = tegra_dma_pause(tdc);
> > +     else
> > +             err = tegra_dma_stop_client(tdc);
> > +
> > +     if (err) {
> > +             raw_spin_unlock_irqrestore(&tdc->lock, flags);
> > +             return err;
> > +     }
> > +
> > +     status = tdc_read(tdc, TEGRA_GPCDMA_CHAN_STATUS);
> > +     if (status & TEGRA_GPCDMA_STATUS_ISE_EOC) {
> > +             dev_dbg(tdc2dev(tdc), "%s():handling isr\n", __func__);
> > +             tegra_dma_xfer_complete(tdc);
> > +             status = tdc_read(tdc, TEGRA_GPCDMA_CHAN_STATUS);
> > +     }
> > +
> > +     wcount = tdc_read(tdc, TEGRA_GPCDMA_CHAN_XFER_COUNT);
> > +     tegra_dma_stop(tdc);
> > +
> > +     tdc->dma_desc->bytes_transferred +=
> > +                     tdc->dma_desc->bytes_requested - (wcount * 4);
> > +
> > +skip_dma_stop:
> > +     tegra_dma_sid_free(tdc);
> > +     vchan_free_chan_resources(&tdc->vc);
> > +     kfree(&tdc->vc);
> 
> You really going to kfree the head of tegra_dma_channel here? Once again, this
> code was 100% untested :/
I did validate this using DMATEST which did not show any error.
https://www.kernel.org/doc/html/latest/driver-api/dmaengine/dmatest.html
Do you suggest something better?

> You're not allowed to free channel from the dma_terminate_all() callback. This
> callback terminates submitted descs, that's it.
> 
Sorry, I am relatively new to DMA framework (probably you get it from the patch 
version no. :)). I read your previous comment as to use tdc->vc instead of dma_desc.
I would learn a bit more and update with a change. Thanks for the inputs.

Thanks,
Akhil

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