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

Christian Bruel
2024-12-05T11:51:40Z

Hello Bjorn and Lucas,

On 11/29/24 22:18, Lucas Stach wrote:
> 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.
>>

agree,

> 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.

far better indeed, dma-ranges works like a charm

thanks,

>
> 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);
>>
>