Re: [PATCH v2 2/5] PCI: stm32: Add PCIe host support for STM32MP25

[Lucas Stach <l.stach@pengutronix.de>]

Am Freitag, dem 29.11.2024 um 14:58 -0600 schrieb Bjorn Helgaas:
> [+to Rob, DMA mask question]
> 
> On Tue, Nov 26, 2024 at 04:51:16PM +0100, Christian Bruel wrote:
> > Add driver for the STM32MP25 SoC PCIe Gen2 controller based on the
> > DesignWare PCIe core.
> 
> Can you include the numeric rate, not just "gen2", so we don't have to
> search for it?
> 
> > +static int stm32_pcie_resume_noirq(struct device *dev)
> > +{
> > +	struct stm32_pcie *stm32_pcie = dev_get_drvdata(dev);
> > +	struct dw_pcie *pci = stm32_pcie->pci;
> > +	struct dw_pcie_rp *pp = &pci->pp;
> > +	int ret;
> > +
> > +	/* init_state must be called first to force clk_req# gpio when no
> > +	 * device is plugged.
> > +	 */
> 
> Use drivers/pci/ conventional comment style:
> 
>   /*
>    * text ...
>    */
> 
> > +static bool is_stm32_pcie_driver(struct device *dev)
> > +{
> > +	/* PCI bridge */
> > +	dev = get_device(dev);
> > +
> > +	/* Platform driver */
> > +	dev = get_device(dev->parent);
> > +
> > +	return (dev->driver == &stm32_pcie_driver.driver);
> > +}
> > +
> > +/*
> > + * DMA masters can only access the first 4GB of memory space,
> > + * so we setup the bus DMA limit accordingly.
> > + */
> > +static int stm32_dma_limit(struct pci_dev *pdev, void *data)
> > +{
> > +	dev_dbg(&pdev->dev, "disabling DMA DAC for device");
> > +
> > +	pdev->dev.bus_dma_limit = DMA_BIT_MASK(32);
> 
> I don't think this is the right way to do this.  Surely there's a way
> to describe the DMA capability of the bridge once instead of iterating
> over all the downstream devices?  This quirk can't work for hot-added
> devices anyway.
> 
This should simply be a dma-ranges property in the PCIe host controller
DT node, which should describe the DMA address range limits for
transactions passing through the host.

Regards,
Lucas

> > +	return 0;
> > +}
> > +
> > +static void quirk_stm32_dma_mask(struct pci_dev *pci)
> > +{
> > +	struct pci_dev *root_port;
> > +
> > +	root_port = pcie_find_root_port(pci);
> > +
> > +	if (root_port && is_stm32_pcie_driver(root_port->dev.parent))
> > +		pci_walk_bus(pci->bus, stm32_dma_limit, NULL);
> > +}
> > +DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_SYNOPSYS, 0x0550, quirk_stm32_dma_mask);
>