linux-kernel - Re: [PATCH 6/7] MIPS: SGI-IP27: use generic PCI driver

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Message-Id: <20190129162445.8584b58862068c0a7693718c@suse.de>
Date:   Tue, 29 Jan 2019 16:24:45 +0100
From:   Thomas Bogendoerfer <tbogendoerfer@...e.de>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        James Hogan <jhogan@...nel.org>, linux-kernel@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-pci@...r.kernel.org,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Paul Burton <paul.burton@...s.com>,
        Ralf Baechle <ralf@...ux-mips.org>
Subject: Re: [PATCH 6/7] MIPS: SGI-IP27: use generic PCI driver

On Mon, 28 Jan 2019 05:32:15 -0800
Christoph Hellwig <hch@...radead.org> wrote:

> > +#ifdef CONFIG_NUMA
> > +int pcibus_to_node(struct pci_bus *bus)
> > +{
> > +	struct bridge_controller *bc = BRIDGE_CONTROLLER(bus);
> > +
> > +	return bc->nasid;
> > +}
> > +EXPORT_SYMBOL(pcibus_to_node);
> > +#endif /* CONFIG_NUMA */
> 
> From an abstraction point of view this doesn't really belong into
> a bridge driver as it is a global exported function.  I guess we can
> keep it here with a fixme comment, but we should probably move this
> into a method call instead.

or put the nodeid into the bus struct ?

> > +dma_addr_t __phys_to_dma(struct device *dev, phys_addr_t paddr)
> > +{
> > +	struct pci_dev *pdev = to_pci_dev(dev);
> > +	struct bridge_controller *bc = BRIDGE_CONTROLLER(pdev->bus);
> > +
> > +	return bc->baddr + paddr;
> > +}
> > +
> > +phys_addr_t __dma_to_phys(struct device *dev, dma_addr_t dma_addr)
> > +{
> > +	return dma_addr & ~(0xffUL << 56);
> > +}
> 
> Similarly here - these are global platform-wide hooks, so having them
> in a pci bridge driver is not the proper abstraction level.
> 
> Note that we could probably fix these by just switching IP27 and
> other users of the bridge chip to use the dma_pfn_offset field
> in struct device and stop overriding these functions.

I'm all for it. I looked at the examples for using dma_pfn_offset and the
only one coming close to usefull for me is arch/sh/drivers/pci/pcie-sh7786.c
It overloads pcibios_bus_add_device() to set dma_pfn_offset, which doesn't
look much nicer. What about having a dma_pfn_offset in struct pci_bus
which all device inherit from ?

Thomas.

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