linux-kernel - RE: [PATCH] dma-mapping: move dma configuration to bus infrastructure

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Date:   Tue, 13 Mar 2018 15:59:58 +0000
From:   Nipun Gupta <nipun.gupta@....com>
To:     Christoph Hellwig <hch@....de>
CC:     "robin.murphy@....com" <robin.murphy@....com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "dmitry.torokhov@...il.com" <dmitry.torokhov@...il.com>,
        "rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>,
        "jarkko.sakkinen@...ux.intel.com" <jarkko.sakkinen@...ux.intel.com>,
        "linus.walleij@...aro.org" <linus.walleij@...aro.org>,
        "johan@...nel.org" <johan@...nel.org>,
        "msuchanek@...e.de" <msuchanek@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: RE: [PATCH] dma-mapping: move dma configuration to bus infrastructure



> -----Original Message-----
> From: Christoph Hellwig [mailto:hch@....de]
> Sent: Tuesday, March 13, 2018 13:05
> > +int amba_dma_configure(struct device *dev)
> > +{
> > +	enum dev_dma_attr attr;
> > +	int ret = 0;
> > +
> > +	if (dev->of_node) {
> > +		ret = of_dma_configure(dev, dev->of_node);
> > +	} else if (has_acpi_companion(dev)) {
> > +		attr = acpi_get_dma_attr(to_acpi_device_node(dev->fwnode));
> > +		if (attr != DEV_DMA_NOT_SUPPORTED)
> > +			ret = acpi_dma_configure(dev, attr);
> > +	}
> > +
> > +	return ret;
> 
> This code sniplet is duplicated so many times that I think we should
> just have some sort of dma_common_configure() for it that the various
> busses can use.

Agree. There is no good point in duplicating the code.
So this new API will be part of 'drivers/base/dma-mapping.c' file?

> 
> > +void amba_dma_deconfigure(struct device *dev)
> > +{
> > +	of_dma_deconfigure(dev);
> > +	acpi_dma_deconfigure(dev);
> > +}
> 
> As mention in my previous reply I think we don't even need a deconfigure
> callback at this point - just remove the ACPI and OF wrappers and
> clear the dma ops.
> 
> Also in this series we should replace the force_dma flag by use of the
> proper method, e.g. give a force parameter to of_dma_configure and the
> new dma_common_configure helper that the busses that want it can set.

I am more inclined to what Robin states in other mail to keep symmetry.
i.e. to keep dma_configure() and dma_deconfigure() and call
dev->bus->dma_configure from dma_configure(). Is this okay?

Thanks,
Nipun