linux-kernel - RE: [PATCH v6 2/4] dmaengine: tegra: Add tegra gpcdma driver

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Date:   Wed, 22 Sep 2021 14:46:50 +0000
From:   Akhil R <akhilrajeev@...dia.com>
To:     Jonathan Hunter <jonathanh@...dia.com>
CC:     "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        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>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        Pavan Kunapuli <pkunapuli@...dia.com>
Subject: RE: [PATCH v6 2/4] dmaengine: tegra: Add tegra gpcdma driver


> On 17/09/2021 15:11, Akhil R wrote:
> > +static int tegra_dma_slave_config(struct dma_chan *dc,
> > +				  struct dma_slave_config *sconfig) {
> > +	struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
> > +
> > +	if (tdc->dma_desc) {
> > +		dev_err(tdc2dev(tdc), "Configuration not allowed\n");
> > +		return -EBUSY;
> > +	}
> > +
> > +	memcpy(&tdc->dma_sconfig, sconfig, sizeof(*sconfig));
> > +	if (tdc->slave_id == -1)
> > +		tdc->slave_id = sconfig->slave_id;
> > +
> > +	tdc->config_init = true;
> > +	return 0;
> > +}
> 
> So you have a function to reserve a slave ID, but you don't check here if it is
> already reserved.
slave-id is reserved considering the direction as well.
'direction' is available only during prep_slave_sg function, I guess.
>
> ...
>
> > +
> > +	iommu_spec = dev_iommu_fwspec_get(&pdev->dev);
> > +	if (!iommu_spec) {
> > +		dev_err(&pdev->dev, "Missing iommu stream-id\n");
> > +		return -EINVAL;
> > +	}
> > +	stream_id = iommu_spec->ids[0] & 0xffff;
> 
> Is it an error if the ID is greater than 0xffff?
The value should correspond to one of the GPC DMA Clients listed in
include/dt-bindings/memory/tegra186-mc.h.
I saw similar masking in other tegra drivers also for stream-id.

Would add fixes for other comments in the next version.

Thanks,
Akhil

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