Re: [PATCH RFC 10/13] dmaengine: sdxi: Add PCI driver support

[Mario Limonciello <mario.limonciello@amd.com>]

On 9/5/2025 1:48 PM, Nathan Lynch via B4 Relay wrote:
> From: Nathan Lynch <nathan.lynch@amd.com>
> 
> Add support for binding to PCIe-hosted SDXI devices. SDXI requires
> MSI(-X) for PCI implementations, so this code will be gated by
> CONFIG_PCI_MSI in the Makefile.
> 
> Co-developed-by: Wei Huang <wei.huang2@amd.com>
> Signed-off-by: Wei Huang <wei.huang2@amd.com>
> Signed-off-by: Nathan Lynch <nathan.lynch@amd.com>
> ---
>   drivers/dma/sdxi/pci.c | 216 +++++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 216 insertions(+)
> 
> diff --git a/drivers/dma/sdxi/pci.c b/drivers/dma/sdxi/pci.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..b7f74555395c605c4affffb198ee359accac8521
> --- /dev/null
> +++ b/drivers/dma/sdxi/pci.c
> @@ -0,0 +1,216 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * SDXI PCI device code
> + *
> + * Copyright (C) 2025 Advanced Micro Devices, Inc.
> + */
> +
> +#include <linux/bitfield.h>
> +#include <linux/bits.h>
> +#include <linux/delay.h>
> +#include <linux/device.h>
> +#include <linux/dev_printk.h>
> +#include <linux/dma-direction.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/errno.h>
> +#include <linux/io.h>
> +#include <linux/iomap.h>
> +#include <linux/math64.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/pci-ats.h>
> +#include <linux/pci.h>
> +
> +#include "mmio.h"
> +#include "sdxi.h"
> +
> +/*
> + * SDXI devices signal message 0 on error conditions, see "Error
> + * Logging Control and Status Registers".
> + */
> +#define ERROR_IRQ_MSG 0
> +
> +/* MMIO BARs */
> +#define MMIO_CTL_REGS_BAR		0x0
> +#define MMIO_DOORBELL_BAR		0x2
> +
> +static struct pci_dev *sdxi_to_pci_dev(const struct sdxi_dev *sdxi)
> +{
> +	return to_pci_dev(sdxi_to_dev(sdxi));
> +}
> +
> +static int sdxi_pci_irq_init(struct sdxi_dev *sdxi)
> +{
> +	struct pci_dev *pdev = sdxi_to_pci_dev(sdxi);
> +	int msi_count;
> +	int ret;
> +
> +	/* 1st irq for error + 1 for each context */
> +	msi_count = sdxi->max_cxts + 1;
> +
> +	ret = pci_alloc_irq_vectors(pdev, 1, msi_count,
> +				    PCI_IRQ_MSI | PCI_IRQ_MSIX);
> +	if (ret < 0) {
> +		sdxi_err(sdxi, "alloc MSI/MSI-X vectors failed\n");
> +		return ret;
> +	}
> +
> +	sdxi->error_irq = pci_irq_vector(pdev, ERROR_IRQ_MSG);
> +
> +	sdxi_dbg(sdxi, "allocated %d irq vectors", ret);
> +
> +	return 0;
> +}
> +
> +static void sdxi_pci_irq_exit(struct sdxi_dev *sdxi)
> +{
> +	pci_free_irq_vectors(sdxi_to_pci_dev(sdxi));
> +}
> +
> +static int sdxi_pci_map(struct sdxi_dev *sdxi)
> +{
> +	struct pci_dev *pdev = sdxi_to_pci_dev(sdxi);
> +	int bars, ret;
> +
> +	bars = 1 << MMIO_CTL_REGS_BAR | 1 << MMIO_DOORBELL_BAR;
> +	ret = pcim_iomap_regions(pdev, bars, SDXI_DRV_NAME);
> +	if (ret) {
> +		sdxi_err(sdxi, "pcim_iomap_regions failed (%d)\n", ret);
> +		return ret;
> +	}
> +
> +	sdxi->dbs_bar = pci_resource_start(pdev, MMIO_DOORBELL_BAR);
> +
> +	/* FIXME: pcim_iomap_table may return NULL, and it's deprecated. */
> +	sdxi->ctrl_regs = pcim_iomap_table(pdev)[MMIO_CTL_REGS_BAR];
> +	sdxi->dbs = pcim_iomap_table(pdev)[MMIO_DOORBELL_BAR];
> +	if (!sdxi->ctrl_regs || !sdxi->dbs) {
> +		sdxi_err(sdxi, "pcim_iomap_table failed\n");
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +static void sdxi_pci_unmap(struct sdxi_dev *sdxi)
> +{
> +	struct pci_dev *pdev = sdxi_to_pci_dev(sdxi);
> +
> +	pcim_iounmap(pdev, sdxi->ctrl_regs);
> +	pcim_iounmap(pdev, sdxi->dbs);
> +}
> +
> +static int sdxi_pci_init(struct sdxi_dev *sdxi)
> +{
> +	struct pci_dev *pdev = sdxi_to_pci_dev(sdxi);
> +	struct device *dev = &pdev->dev;
> +	int dma_bits = 64;
> +	int ret;
> +
> +	ret = pcim_enable_device(pdev);
> +	if (ret) {
> +		sdxi_err(sdxi, "pcim_enbale_device failed\n");
> +		return ret;
> +	}
> +
> +	pci_set_master(pdev);

Does pci_set_master() need to come before dma_set_mask_and_coherent() 
and sdxi_pci_map()?

If so; there should be an error handling path that does pci_clear_master().

> +	ret = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(dma_bits));
> +	if (ret) {
> +		sdxi_err(sdxi, "failed to set DMA mask & coherent bits\n");
> +		return ret;
> +	}
> +
> +	ret = sdxi_pci_map(sdxi);
> +	if (ret) {
> +		sdxi_err(sdxi, "failed to map device IO resources\n");
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static void sdxi_pci_exit(struct sdxi_dev *sdxi)
> +{
> +	sdxi_pci_unmap(sdxi);

I think you need a pci_clear_master() here.

> +}
> +
> +static struct sdxi_dev *sdxi_device_alloc(struct device *dev)
> +{
> +	struct sdxi_dev *sdxi;
> +
> +	sdxi = kzalloc(sizeof(*sdxi), GFP_KERNEL);
> +	if (!sdxi)
> +		return NULL;
> +
> +	sdxi->dev = dev;
> +
> +	mutex_init(&sdxi->cxt_lock);
> +
> +	return sdxi;
> +}
> +
> +static void sdxi_device_free(struct sdxi_dev *sdxi)
> +{
> +	kfree(sdxi);
> +}
> +
> +static const struct sdxi_dev_ops sdxi_pci_dev_ops = {
> +	.irq_init = sdxi_pci_irq_init,
> +	.irq_exit = sdxi_pci_irq_exit,
> +};
> +
> +static int sdxi_pci_probe(struct pci_dev *pdev,
> +			  const struct pci_device_id *id)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct sdxi_dev *sdxi;
> +	int err;
> +
> +	sdxi = sdxi_device_alloc(dev);
> +	if (!sdxi)
> +		return -ENOMEM;
> +
> +	pci_set_drvdata(pdev, sdxi);
> +
> +	err = sdxi_pci_init(sdxi);
> +	if (err)
> +		goto free_sdxi;
> +
> +	err = sdxi_device_init(sdxi, &sdxi_pci_dev_ops);
> +	if (err)
> +		goto pci_exit;
> +
> +	return 0;
> +
> +pci_exit:
> +	sdxi_pci_exit(sdxi);
> +free_sdxi:
> +	sdxi_device_free(sdxi);
> +
> +	return err;
> +}
> +
> +static void sdxi_pci_remove(struct pci_dev *pdev)
> +{
> +	struct sdxi_dev *sdxi = pci_get_drvdata(pdev);
> +
> +	sdxi_device_exit(sdxi);
> +	sdxi_pci_exit(sdxi);
> +	sdxi_device_free(sdxi);
> +}
> +
> +static const struct pci_device_id sdxi_id_table[] = {
> +	{ PCI_DEVICE_CLASS(PCI_CLASS_ACCELERATOR_SDXI, 0xffffff) },
> +	{0, }
> +};
> +MODULE_DEVICE_TABLE(pci, sdxi_id_table);
> +
> +static struct pci_driver sdxi_driver = {
> +	.name = "sdxi",
> +	.id_table = sdxi_id_table,
> +	.probe = sdxi_pci_probe,
> +	.remove = sdxi_pci_remove,
> +	.sriov_configure = pci_sriov_configure_simple,
> +};
> +
> +module_pci_driver(sdxi_driver);
>