linux-kernel - Re: [PATCH v2 23/26] dmaengine: dw-edma: Bypass dma-ranges mapping for the local setup

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Message-ID: <20220525085621.xvxnbvsddp6uqwpm@mobilestation>
Date:   Wed, 25 May 2022 11:56:21 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Vinod Koul <vkoul@...nel.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Frank Li <Frank.Li@....com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        linux-pci@...r.kernel.org, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 23/26] dmaengine: dw-edma: Bypass dma-ranges mapping
 for the local setup

On Tue, May 24, 2022 at 06:49:59PM +0530, Manivannan Sadhasivam wrote:
> On Wed, May 04, 2022 at 01:51:01AM +0300, Serge Semin wrote:
> > DW eDMA doesn't perform any translation of the traffic generated on the
> > CPU/Application side. It just generates read/write AXI-bus requests with
> > the specified addresses. But in case if the dma-ranges DT-property is
> > specified for a platform device node, Linux will use it to map the CPU
> > memory regions into the DMAable bus ranges. This isn't what we want for
> > the eDMA embedded into the locally accessed DW PCIe Root Port and
> > End-point. In order to work that around let's set the chan_dma_dev flag
> > for each DW eDMA channel thus forcing the client drivers to getting a
> > custom dma-ranges-less parental device for the mappings.
> > 
> > Note it will only work for the client drivers using the
> > dmaengine_get_dma_device() method to get the parental DMA device.
> > 
> > Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> > Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > 
> > ---
> > 
> > Changelog v2:
> > - Fix the comment a bit to being clearer. (@Manivannan)
> > ---
> >  drivers/dma/dw-edma/dw-edma-core.c | 15 +++++++++++++++
> >  1 file changed, 15 insertions(+)
> > 
> > diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
> > index 6a8282eaebaf..908607785401 100644
> > --- a/drivers/dma/dw-edma/dw-edma-core.c
> > +++ b/drivers/dma/dw-edma/dw-edma-core.c
> > @@ -716,6 +716,21 @@ static int dw_edma_alloc_chan_resources(struct dma_chan *dchan)
> >  	if (chan->status != EDMA_ST_IDLE)
> >  		return -EBUSY;
> >  
> > +	/* Bypass the dma-ranges based memory regions mapping for the eDMA
> > +	 * controlled from the CPU/Application side since in that case
> > +	 * the local memory address is left untranslated.
> > +	 */
> > +	if (chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL) {
> > +		dchan->dev->chan_dma_dev = true;
> > +
> > +		dchan->dev->device.dma_coherent = chan->dw->chip->dev->dma_coherent;
> 

> I happen to test this series on Qcom ARM32 machine and it errors out during the
> compilation due to "dma_coherent" not available on !SWIOTLB ARM32 configs.

Nice catch! Thanks. I'll fix it in the next patchset version.

-Sergey

> 
> Thanks,
> Mani
> 
> > +		dma_coerce_mask_and_coherent(&dchan->dev->device,
> > +					     dma_get_mask(chan->dw->chip->dev));
> > +		dchan->dev->device.dma_parms = chan->dw->chip->dev->dma_parms;
> > +	} else {
> > +		dchan->dev->chan_dma_dev = false;
> > +	}
> > +
> >  	pm_runtime_get(chan->dw->chip->dev);
> >  
> >  	return 0;
> > -- 
> > 2.35.1
> > 
> 
> -- 
> மணிவண்ணன் சதாசிவம்