Message-ID: <ZxJ7HoSuYNr8mwSi@lizhi-Precision-Tower-5810>
Date: Fri, 18 Oct 2024 11:13:34 -0400
From: Frank Li <Frank.li@....com>
To: Niklas Cassel <cassel@...nel.org>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>, Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	imx@...ts.linux.dev, dlemoal@...nel.org, maz@...nel.org,
	tglx@...utronix.de, jdmason@...zu.us
Subject: Re: [PATCH v3 4/6] PCI: endpoint: pci-epf-test: Add doorbell test
 support

On Fri, Oct 18, 2024 at 04:01:05PM +0200, Niklas Cassel wrote:
> Hello Frank,
>
> On Tue, Oct 15, 2024 at 06:07:17PM -0400, Frank Li wrote:
> > Add three registers: doorbell_bar, doorbell_addr, and doorbell_data,
> > along with doorbell_done. Use pci_epf_alloc_doorbell() to allocate a
> > doorbell address space.
> >
> > Enable the Root Complex (RC) side driver to trigger pci-epc-test's doorbell
> > callback handler by writing doorbell_data to the mapped doorbell_bar's
> > address space.
> >
> > Set doorbell_done in the doorbell callback to indicate completion.
> >
> > To avoid broken compatibility, use new PID/VID and set RevID bigger than 0.
> > So only new pcitest program can distinguish with/without doorbell support
> > and avoid wrongly write test data to doorbell bar.
> >
> > Signed-off-by: Frank Li <Frank.Li@....com>
> > ---
> >  drivers/pci/endpoint/functions/pci-epf-test.c | 58 ++++++++++++++++++++++++++-
> >  1 file changed, 56 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c b/drivers/pci/endpoint/functions/pci-epf-test.c
> > index 7c2ed6eae53ad..c054d621353a6 100644
> > --- a/drivers/pci/endpoint/functions/pci-epf-test.c
> > +++ b/drivers/pci/endpoint/functions/pci-epf-test.c
> > @@ -11,12 +11,14 @@
> >  #include <linux/dmaengine.h>
> >  #include <linux/io.h>
> >  #include <linux/module.h>
> > +#include <linux/msi.h>
> >  #include <linux/slab.h>
> >  #include <linux/pci_ids.h>
> >  #include <linux/random.h>
> >
> >  #include <linux/pci-epc.h>
> >  #include <linux/pci-epf.h>
> > +#include <linux/pci-ep-msi.h>
> >  #include <linux/pci_regs.h>
> >
> >  #define IRQ_TYPE_INTX			0
> > @@ -39,6 +41,7 @@
> >  #define STATUS_IRQ_RAISED		BIT(6)
> >  #define STATUS_SRC_ADDR_INVALID		BIT(7)
> >  #define STATUS_DST_ADDR_INVALID		BIT(8)
> > +#define STATUS_DOORBELL_SUCCESS		BIT(9)
> >
> >  #define FLAG_USE_DMA			BIT(0)
> >
> > @@ -50,6 +53,7 @@ struct pci_epf_test {
> >  	void			*reg[PCI_STD_NUM_BARS];
> >  	struct pci_epf		*epf;
> >  	enum pci_barno		test_reg_bar;
> > +	enum pci_barno		doorbell_bar;
> >  	size_t			msix_table_offset;
> >  	struct delayed_work	cmd_handler;
> >  	struct dma_chan		*dma_chan_tx;
> > @@ -74,6 +78,9 @@ struct pci_epf_test_reg {
> >  	u32	irq_type;
> >  	u32	irq_number;
> >  	u32	flags;
> > +	u32	doorbell_bar;
> > +	u32	doorbell_addr;
> > +	u32	doorbell_data;
> >  } __packed;
> >
> >  static struct pci_epf_header test_header = {
> > @@ -695,7 +702,7 @@ static int pci_epf_test_set_bar(struct pci_epf *epf)
> >  	enum pci_barno test_reg_bar = epf_test->test_reg_bar;
> >
> >  	for (bar = 0; bar < PCI_STD_NUM_BARS; bar++) {
> > -		if (!epf_test->reg[bar])
> > +		if (!epf_test->reg[bar] && bar != epf_test->doorbell_bar)
> >  			continue;
> >
> >  		ret = pci_epc_set_bar(epc, epf->func_no, epf->vfunc_no,
> > @@ -810,11 +817,24 @@ static int pci_epf_test_link_down(struct pci_epf *epf)
> >  	return 0;
> >  }
> >
> > +static int pci_epf_test_doorbell(struct pci_epf *epf, int index)
> > +{
> > +	struct pci_epf_test *epf_test = epf_get_drvdata(epf);
> > +	enum pci_barno test_reg_bar = epf_test->test_reg_bar;
> > +	struct pci_epf_test_reg *reg = epf_test->reg[test_reg_bar];
> > +
> > +	reg->status |= STATUS_DOORBELL_SUCCESS;
> > +	pci_epf_test_raise_irq(epf_test, reg);
> > +
> > +	return 0;
> > +}
> > +
> >  static const struct pci_epc_event_ops pci_epf_test_event_ops = {
> >  	.epc_init = pci_epf_test_epc_init,
> >  	.epc_deinit = pci_epf_test_epc_deinit,
> >  	.link_up = pci_epf_test_link_up,
> >  	.link_down = pci_epf_test_link_down,
> > +	.doorbell = pci_epf_test_doorbell,
> >  };
> >
> >  static int pci_epf_test_alloc_space(struct pci_epf *epf)
> > @@ -853,7 +873,7 @@ static int pci_epf_test_alloc_space(struct pci_epf *epf)
> >  		if (bar == NO_BAR)
> >  			break;
> >
> > -		if (bar == test_reg_bar)
> > +		if (bar == test_reg_bar || bar == epf_test->doorbell_bar)
> >  			continue;
> >
> >  		base = pci_epf_alloc_space(epf, bar_size[bar], bar,
> > @@ -887,7 +907,11 @@ static int pci_epf_test_bind(struct pci_epf *epf)
> >  	struct pci_epf_test *epf_test = epf_get_drvdata(epf);
> >  	const struct pci_epc_features *epc_features;
> >  	enum pci_barno test_reg_bar = BAR_0;
> > +	enum pci_barno doorbell_bar = NO_BAR;
> >  	struct pci_epc *epc = epf->epc;
> > +	struct msi_msg *msg;
> > +	u64 doorbell_addr;
> > +	u32 align;
> >
> >  	if (WARN_ON_ONCE(!epc))
> >  		return -EINVAL;
> > @@ -905,10 +929,40 @@ static int pci_epf_test_bind(struct pci_epf *epf)
> >  	epf_test->test_reg_bar = test_reg_bar;
> >  	epf_test->epc_features = epc_features;
> >
> > +	align = epc_features->align;
> > +	align = align ? align : 128;
> > +
> > +	/* Only revid >=1 support RC-to-EP Door bell */
> > +	ret = epf->header->revid > 0 ?  pci_epf_alloc_doorbell(epf, 1) : -EINVAL;
>
> I really, really don't like this idea.
>
> This means that you would need to write a revid > 1 in configfs to test this.
> I also don't think that it is right that pci-epf-test takes ownership of "rev".
>
> How about something like this instead:
>
> My thinking is that you add a doorbell_capable struct member to epc_features,
> and then populate CAPS_DOORBELL_SUPPORT based on epc_features in
> pci_epf_test_init_caps() (similar to how my proposal sets CAPS_MSI_SUPPORT).

The primary issue is that the doorbell is not a capability of the EPC
itself; rather, it's a capability of the entire system that requires an
external MSI/ITS controller. The CAPS_DOORBELL_SUPPORT should handle this
feature. Even we needn't CAPS_DOORBELL_SUPPORT, just call
pci_epf_alloc_doorbell(), if error return, means not support DOORBELL.

One potential problem is that if the EPC supports CAPS_DOORBELL_SUPPORT,
but the user continues to use older PID/VID values to enable EPF testing,
the pcitest tool may treat the doorbell BAR as a normal BAR. This could
lead to confusion for users as to why their system breaks after a kernel
update.

To use the doorbell functionality, the revid can clearly inform users that
this feature breaks previous compatibility. Users will need to update the
host-side driver, PID/VID values, and the pcitest tools accordingly.

Frank

>
>
> From 0f6bb535c6d56e03e9b3550194deec04a1c1d370 Mon Sep 17 00:00:00 2001
> From: Niklas Cassel <cassel@...nel.org>
> Date: Fri, 18 Oct 2024 10:32:39 +0200
> Subject: [PATCH] PCI: endpoint: pci-epf-test: Add support for exposing EPC
>  capabilities
>
> Currently, there is no way for the pci-endpoint-test driver (RC side),
> to know which features the EPC supports.
>
> Expose some of the EPC:s capabilities in the test_reg_bar, such that
> the pci-endpoint-test driver can know if a feature (e.g. MSI-X or DMA)
> is supported before attempting to test it.
>
> Signed-off-by: Niklas Cassel <cassel@...nel.org>
> ---
>  drivers/misc/pci_endpoint_test.c              | 34 +++++++++++++++
>  drivers/pci/endpoint/functions/pci-epf-test.c | 43 +++++++++++++++++++
>  2 files changed, 77 insertions(+)
>
> diff --git a/drivers/misc/pci_endpoint_test.c b/drivers/misc/pci_endpoint_test.c
> index 3aaaf47fa4ee..7eb045dc81b6 100644
> --- a/drivers/misc/pci_endpoint_test.c
> +++ b/drivers/misc/pci_endpoint_test.c
> @@ -69,6 +69,20 @@
>  #define PCI_ENDPOINT_TEST_FLAGS			0x2c
>  #define FLAG_USE_DMA				BIT(0)
>
> +#define CAPS_MAGIC				0x25ccf687
> +#define PCI_ENDPOINT_TEST_CAPS_MAGIC		0x30
> +#define PCI_ENDPOINT_TEST_CAPS_VERSION		0x34
> +#define PCI_ENDPOINT_TEST_CAPS			0x38
> +
> +#define CAPS_MSI_SUPPORT		BIT(0)
> +#define CAPS_MSIX_SUPPORT		BIT(1)
> +#define CAPS_DMA_SUPPORT		BIT(2)
> +#define CAPS_DMA_IS_PRIVATE		BIT(3) /* only valid if DMA_SUPPORT */
> +#define CAPS_DOORBELL_SUPPORT		BIT(4)
> +#define CAPS_DOORBELL_BAR_MASK		GENMASK(7, 5) /* only valid if DOORBELL_SUPPORT */
> +#define CAPS_DOORBELL_BAR_SHIFT		5
> +#define CAPS_DOORBELL_BAR(x)		(((x) & CAPS_DOORBELL_BAR_MASK) >> CAPS_DOORBELL_BAR_SHIFT)
> +
>  #define PCI_DEVICE_ID_TI_AM654			0xb00c
>  #define PCI_DEVICE_ID_TI_J7200			0xb00f
>  #define PCI_DEVICE_ID_TI_AM64			0xb010
> @@ -805,6 +819,24 @@ static const struct file_operations pci_endpoint_test_fops = {
>  	.unlocked_ioctl = pci_endpoint_test_ioctl,
>  };
>
> +static void pci_endpoint_get_caps(struct pci_endpoint_test *test)
> +{
> +	u32 caps_magic, caps;
> +
> +	/* check if endpoint has CAPS support */
> +	caps_magic = pci_endpoint_test_readl(test, PCI_ENDPOINT_TEST_CAPS_MAGIC);
> +	if (caps_magic != CAPS_MAGIC)
> +		return;
> +
> +	caps = pci_endpoint_test_readl(test, PCI_ENDPOINT_TEST_CAPS);
> +	pr_info("CAPS: MSI support: %u\n", (caps & CAPS_MSI_SUPPORT) ? 1 : 0);
> +	pr_info("CAPS: MSI-X support: %u\n", (caps & CAPS_MSIX_SUPPORT) ? 1 : 0);
> +	pr_info("CAPS: DMA support: %u\n", (caps & CAPS_DMA_SUPPORT) ? 1 : 0);
> +	pr_info("CAPS: DMA is private: %u\n", (caps & CAPS_DMA_IS_PRIVATE) ? 1 : 0);
> +	pr_info("CAPS: DOORBELL support: %u\n", (caps & CAPS_DOORBELL_SUPPORT) ? 1 : 0);
> +	pr_info("CAPS: DOORBELL BAR: %lu\n", CAPS_DOORBELL_BAR(caps));
> +}
> +
>  static int pci_endpoint_test_probe(struct pci_dev *pdev,
>  				   const struct pci_device_id *ent)
>  {
> @@ -906,6 +938,8 @@ static int pci_endpoint_test_probe(struct pci_dev *pdev,
>  		goto err_kfree_test_name;
>  	}
>
> +	pci_endpoint_get_caps(test);
> +
>  	misc_device = &test->miscdev;
>  	misc_device->minor = MISC_DYNAMIC_MINOR;
>  	misc_device->name = kstrdup(name, GFP_KERNEL);
> diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c b/drivers/pci/endpoint/functions/pci-epf-test.c
> index a73bc0771d35..2dd90e2e8565 100644
> --- a/drivers/pci/endpoint/functions/pci-epf-test.c
> +++ b/drivers/pci/endpoint/functions/pci-epf-test.c
> @@ -44,6 +44,18 @@
>
>  #define TIMER_RESOLUTION		1
>
> +#define CAPS_MAGIC			0x25ccf687
> +#define CAPS_VERSION			0x1
> +
> +#define CAPS_MSI_SUPPORT		BIT(0)
> +#define CAPS_MSIX_SUPPORT		BIT(1)
> +#define CAPS_DMA_SUPPORT		BIT(2)
> +#define CAPS_DMA_IS_PRIVATE		BIT(3) /* only valid if DMA_SUPPORT */
> +#define CAPS_DOORBELL_SUPPORT		BIT(4)
> +#define CAPS_DOORBELL_BAR_MASK		GENMASK(7, 5) /* only valid if DOORBELL_SUPPORT */
> +#define CAPS_DOORBELL_BAR_SHIFT		5
> +#define CAPS_DOORBELL_BAR(x)		(((x) & CAPS_DOORBELL_BAR_MASK) >> CAPS_DOORBELL_BAR_SHIFT)
> +
>  static struct workqueue_struct *kpcitest_workqueue;
>
>  struct pci_epf_test {
> @@ -74,6 +86,9 @@ struct pci_epf_test_reg {
>  	u32	irq_type;
>  	u32	irq_number;
>  	u32	flags;
> +	u32	caps_magic;
> +	u32	caps_version;
> +	u32	caps;
>  } __packed;
>
>  static struct pci_epf_header test_header = {
> @@ -741,6 +756,32 @@ static void pci_epf_test_clear_bar(struct pci_epf *epf)
>  	}
>  }
>
> +static void pci_epf_test_init_caps(struct pci_epf *epf)
> +{
> +	struct pci_epf_test *epf_test = epf_get_drvdata(epf);
> +	const struct pci_epc_features *epc_features = epf_test->epc_features;
> +	enum pci_barno test_reg_bar = epf_test->test_reg_bar;
> +	struct pci_epf_test_reg *reg = epf_test->reg[test_reg_bar];
> +	u32 caps = 0;
> +
> +	reg->caps_magic = cpu_to_le32(CAPS_MAGIC);
> +	reg->caps_version = cpu_to_le32(CAPS_VERSION);
> +
> +	if (epc_features->msi_capable)
> +		caps |= CAPS_MSI_SUPPORT;
> +
> +	if (epc_features->msix_capable)
> +		caps |= CAPS_MSIX_SUPPORT;
> +
> +	if (epf_test->dma_supported)
> +		caps |= CAPS_DMA_SUPPORT;
> +
> +	if (epf_test->dma_private)
> +		caps |= CAPS_DMA_IS_PRIVATE;
> +
> +	reg->caps = cpu_to_le64(caps);
> +}
> +
>  static int pci_epf_test_epc_init(struct pci_epf *epf)
>  {
>  	struct pci_epf_test *epf_test = epf_get_drvdata(epf);
> @@ -765,6 +806,8 @@ static int pci_epf_test_epc_init(struct pci_epf *epf)
>  		}
>  	}
>
> +	pci_epf_test_init_caps(epf);
> +
>  	ret = pci_epf_test_set_bar(epf);
>  	if (ret)
>  		return ret;
> --
> 2.47.0
>

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