Date:   Tue, 25 Feb 2020 19:02:40 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     sathyanarayanan.kuppuswamy@...ux.intel.com
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        ashok.raj@...el.com
Subject: Re: [PATCH v15 3/5] PCI/EDR: Export AER, DPC and error recovery
 functions

On Thu, Feb 13, 2020 at 10:20:15AM -0800, sathyanarayanan.kuppuswamy@...ux.intel.com wrote:
> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> 
> This is a preparatory patch for adding EDR support.
> 
> As per the Downstream Port Containment Related Enhancements ECN to the
> PCI Firmware Specification r3.2, sec 4.5.1, table 4-6, If DPC is
> controlled by firmware, firmware is responsible for initializing
> Downstream Port Containment Extended Capability Structures per firmware
> policy. Further, the OS is permitted to read or write DPC Control and
> Status registers of a port while processing an Error Disconnect Recover
> notification from firmware on that port. Error Disconnect Recover
> notification processing begins with the Error Disconnect Recover notify
> from Firmware, and ends when the OS releases DPC by clearing the DPC
> Trigger Status bit.Firmware can read DPC Trigger Status bit to determine
> the ownership of DPC Control and Status registers. Firmware is not
> permitted to write to DPC Control and Status registers if DPC Trigger
> Status is set i.e. the link is in DPC state. Outside of the Error
> Disconnect Recover notification processing window, the OS is not
> permitted to modify DPC Control or Status registers; only firmware
> is allowed to.
> 
> To add EDR support we need to re-use some of the existing DPC,
> AER and pCIE error recovery functions. So add necessary interfaces.
> 
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> ---
>  drivers/pci/pci.h      |  8 ++++
>  drivers/pci/pcie/aer.c | 39 ++++++++++++++------
>  drivers/pci/pcie/dpc.c | 84 +++++++++++++++++++++++++-----------------
>  drivers/pci/pcie/dpc.h | 20 ++++++++++
>  drivers/pci/pcie/err.c | 30 ++++++++++++---
>  5 files changed, 131 insertions(+), 50 deletions(-)
>  create mode 100644 drivers/pci/pcie/dpc.h
> 
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 6394e7746fb5..136f27cf3871 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -443,6 +443,9 @@ struct aer_err_info {
>  
>  int aer_get_device_error_info(struct pci_dev *dev, struct aer_err_info *info);
>  void aer_print_error(struct pci_dev *dev, struct aer_err_info *info);
> +int pci_aer_clear_err_uncor_status(struct pci_dev *dev);
> +void pci_aer_clear_err_fatal_status(struct pci_dev *dev);
> +int pci_aer_clear_err_status_regs(struct pci_dev *dev);
>  #endif	/* CONFIG_PCIEAER */
>  
>  #ifdef CONFIG_PCIE_DPC
> @@ -549,6 +552,11 @@ static inline int pci_dev_specific_disable_acs_redir(struct pci_dev *dev)
>  /* PCI error reporting and recovery */
>  void pcie_do_recovery(struct pci_dev *dev, enum pci_channel_state state,
>  		      u32 service);
> +pci_ers_result_t pcie_do_recovery_common(struct pci_dev *dev,
> +				enum pci_channel_state state,
> +				u32 service,
> +				pci_ers_result_t (*reset_cb)(void *cb_data),
> +				void *cb_data);
>  
>  bool pcie_wait_for_link(struct pci_dev *pdev, bool active);
>  #ifdef CONFIG_PCIEASPM
> diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
> index 4a818b07a1af..399836aa07f4 100644
> --- a/drivers/pci/pcie/aer.c
> +++ b/drivers/pci/pcie/aer.c
> @@ -376,7 +376,7 @@ void pci_aer_clear_device_status(struct pci_dev *dev)
>  	pcie_capability_write_word(dev, PCI_EXP_DEVSTA, sta);
>  }
>  
> -int pci_cleanup_aer_uncorrect_error_status(struct pci_dev *dev)
> +int pci_aer_clear_err_uncor_status(struct pci_dev *dev)
>  {
>  	int pos;
>  	u32 status, sev;
> @@ -385,9 +385,6 @@ int pci_cleanup_aer_uncorrect_error_status(struct pci_dev *dev)
>  	if (!pos)
>  		return -EIO;
>  
> -	if (pcie_aer_get_firmware_first(dev))
> -		return -EIO;
> -
>  	/* Clear status bits for ERR_NONFATAL errors only */
>  	pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_STATUS, &status);
>  	pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_SEVER, &sev);
> @@ -397,9 +394,17 @@ int pci_cleanup_aer_uncorrect_error_status(struct pci_dev *dev)
>  
>  	return 0;
>  }
> +
> +int pci_cleanup_aer_uncorrect_error_status(struct pci_dev *dev)
> +{
> +	if (pcie_aer_get_firmware_first(dev))
> +		return -EIO;
> +
> +	return pci_aer_clear_err_uncor_status(dev);
> +}
>  EXPORT_SYMBOL_GPL(pci_cleanup_aer_uncorrect_error_status);
>  
> -void pci_aer_clear_fatal_status(struct pci_dev *dev)
> +void pci_aer_clear_err_fatal_status(struct pci_dev *dev)
>  {
>  	int pos;
>  	u32 status, sev;
> @@ -408,9 +413,6 @@ void pci_aer_clear_fatal_status(struct pci_dev *dev)
>  	if (!pos)
>  		return;
>  
> -	if (pcie_aer_get_firmware_first(dev))
> -		return;
> -
>  	/* Clear status bits for ERR_FATAL errors only */
>  	pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_STATUS, &status);
>  	pci_read_config_dword(dev, pos + PCI_ERR_UNCOR_SEVER, &sev);
> @@ -419,7 +421,15 @@ void pci_aer_clear_fatal_status(struct pci_dev *dev)
>  		pci_write_config_dword(dev, pos + PCI_ERR_UNCOR_STATUS, status);
>  }
>  
> -int pci_cleanup_aer_error_status_regs(struct pci_dev *dev)
> +void pci_aer_clear_fatal_status(struct pci_dev *dev)
> +{
> +	if (pcie_aer_get_firmware_first(dev))
> +		return;
> +
> +	return pci_aer_clear_err_fatal_status(dev);
> +}
> +
> +int pci_aer_clear_err_status_regs(struct pci_dev *dev)
>  {
>  	int pos;
>  	u32 status;
> @@ -432,9 +442,6 @@ int pci_cleanup_aer_error_status_regs(struct pci_dev *dev)
>  	if (!pos)
>  		return -EIO;
>  
> -	if (pcie_aer_get_firmware_first(dev))
> -		return -EIO;
> -
>  	port_type = pci_pcie_type(dev);
>  	if (port_type == PCI_EXP_TYPE_ROOT_PORT) {
>  		pci_read_config_dword(dev, pos + PCI_ERR_ROOT_STATUS, &status);
> @@ -450,6 +457,14 @@ int pci_cleanup_aer_error_status_regs(struct pci_dev *dev)
>  	return 0;
>  }
>  
> +int pci_cleanup_aer_error_status_regs(struct pci_dev *dev)
> +{
> +	if (pcie_aer_get_firmware_first(dev))
> +		return -EIO;
> +
> +	return pci_aer_clear_err_status_regs(dev);
> +}

We started with these:

  pci_cleanup_aer_uncorrect_error_status()
  pci_aer_clear_fatal_status()
  pci_cleanup_aer_error_status_regs()

This was already a mess.  They do basically similar things, but the
function names are a complete jumble.  Let's start with preliminary
patches to name them consistently, e.g.,

  pci_aer_clear_nonfatal_status()
  pci_aer_clear_fatal_status()
  pci_aer_clear_status()

Now, for EDR you eventually add this in edr_handle_event():

  edr_handle_event()
  {
    ...
    pci_aer_clear_err_uncor_status(pdev);
    pci_aer_clear_err_fatal_status(pdev);
    pci_aer_clear_err_status_regs(pdev);

I see that this path needs to clear the status even in the
firmware-first case, so you do need some change for that.  But
pci_aer_clear_err_status_regs() does exactly the same thing as
pci_aer_clear_err_uncor_status() and pci_aer_clear_err_fatal_status()
plus a little more (clearing PCI_ERR_ROOT_STATUS), so it should be
sufficient to just call pci_aer_clear_err_status_regs().

So I don't think you need to make wrappers for
pci_aer_clear_nonfatal_status() and pci_aer_clear_fatal_status() at
all since they're not needed by the EDR path.

You *do* need a wrapper for pci_aer_clear_status(), but instead of
just adding random words ("err", "regs") to the name, please name it
something like pci_aer_raw_clear_status() as a hint that it skips
some sort of check.

I would split this into a separate patch.  This patch contains a bunch
of things that aren't really related except that they're needed for
EDR.  I think it will be more readable if each patch just does one
piece of it.

>  void pci_save_aer_state(struct pci_dev *dev)
>  {
>  	struct pci_cap_saved_state *save_state;
> diff --git a/drivers/pci/pcie/dpc.c b/drivers/pci/pcie/dpc.c
> index 99fca8400956..acae12dbf9ff 100644
> --- a/drivers/pci/pcie/dpc.c
> +++ b/drivers/pci/pcie/dpc.c
> @@ -15,15 +15,9 @@
>  #include <linux/pci.h>
>  
>  #include "portdrv.h"
> +#include "dpc.h"
>  #include "../pci.h"
>  
> -struct dpc_dev {
> -	struct pci_dev		*pdev;
> -	u16			cap_pos;
> -	bool			rp_extensions;
> -	u8			rp_log_size;
> -};

Adding dpc.h shouldn't be in this patch because there's no need for a
separate dpc.h file yet -- it's only included this one place.  I'm not
positive a dpc.h is needed at all -- see comments on patch [4/5].

>  static const char * const rp_pio_error_string[] = {
>  	"Configuration Request received UR Completion",	 /* Bit Position 0  */
>  	"Configuration Request received CA Completion",	 /* Bit Position 1  */
> @@ -117,36 +111,44 @@ static int dpc_wait_rp_inactive(struct dpc_dev *dpc)
>  	return 0;
>  }
>  
> -static pci_ers_result_t dpc_reset_link(struct pci_dev *pdev)
> +pci_ers_result_t dpc_reset_link_common(struct dpc_dev *dpc)
>  {

I don't see why you need to split this into dpc_reset_link_common()
and dpc_reset_link().  IIUC, you split it so the DPC driver path can
supply a pci_dev * via

  dpc_handler
    pcie_do_recovery
      pcie_do_recovery_common(..., NULL, NULL)
        reset_link(..., NULL, NULL)
          driver->reset_link(pdev)
            dpc_reset_link(pdev)
              dpc = to_dpc_dev(pdev)
              dpc_reset_link_common(dpc)

while the EDR path can supply a dpc_dev * via

  edr_handle_event
    pcie_do_recovery_common(..., edr_dpc_reset_link, dpc)
      reset_link(..., edr_dpc_reset_link, dpc)
        edr_dpc_reset_link(dpc)
          dpc_reset_link_common(dpc)

But it looks like you *could* make these paths look like:

  dpc_handler
    pcie_do_recovery
      pcie_do_recovery_common(..., NULL, NULL)
        reset_link(..., NULL, NULL)
          driver->reset_link(pdev)
            dpc_reset_link(pdev)

  edr_handle_event
    pcie_do_recovery_common(..., dpc_reset_link, pdev)
      reset_link(..., dpc_reset_link, pdev)
        dpc_reset_link(pdev)

and you wouldn't need edr_dpc_reset_link() at all and you wouldn't
have to split dpc_reset_link_common() out.

> -	struct dpc_dev *dpc;
>  	u16 cap;
>  
> -	/*
> -	 * DPC disables the Link automatically in hardware, so it has
> -	 * already been reset by the time we get here.
> -	 */
> -	dpc = to_dpc_dev(pdev);
>  	cap = dpc->cap_pos;
>  
>  	/*
>  	 * Wait until the Link is inactive, then clear DPC Trigger Status
>  	 * to allow the Port to leave DPC.
>  	 */
> -	pcie_wait_for_link(pdev, false);
> +	pcie_wait_for_link(dpc->pdev, false);

I'm hoping you don't need to split this out at all, but if you do,
adding

  struct pci_dev *pdev = dpc->pdev;

at the top will avoid these needless diffs.

>  	if (dpc->rp_extensions && dpc_wait_rp_inactive(dpc))
>  		return PCI_ERS_RESULT_DISCONNECT;
>  
> -	pci_write_config_word(pdev, cap + PCI_EXP_DPC_STATUS,
> +	pci_write_config_word(dpc->pdev, cap + PCI_EXP_DPC_STATUS,
>  			      PCI_EXP_DPC_STATUS_TRIGGER);
>  
> -	if (!pcie_wait_for_link(pdev, true))
> +	if (!pcie_wait_for_link(dpc->pdev, true))
>  		return PCI_ERS_RESULT_DISCONNECT;
>  
>  	return PCI_ERS_RESULT_RECOVERED;
>  }
>  
> +static pci_ers_result_t dpc_reset_link(struct pci_dev *pdev)
> +{
> +	struct dpc_dev *dpc;
> +
> +	/*
> +	 * DPC disables the Link automatically in hardware, so it has
> +	 * already been reset by the time we get here.
> + 	 */
> +	dpc = to_dpc_dev(pdev);
> +
> +	return dpc_reset_link_common(dpc);
> +
> +}
> +
>  static void dpc_process_rp_pio_error(struct dpc_dev *dpc)
>  {
>  	struct pci_dev *pdev = dpc->pdev;
> @@ -224,10 +226,9 @@ static int dpc_get_aer_uncorrect_severity(struct pci_dev *dev,
>  	return 1;
>  }
>  
> -static irqreturn_t dpc_handler(int irq, void *context)
> +void dpc_process_error(struct dpc_dev *dpc)
>  {
>  	struct aer_err_info info;
> -	struct dpc_dev *dpc = context;
>  	struct pci_dev *pdev = dpc->pdev;
>  	u16 cap = dpc->cap_pos, status, source, reason, ext_reason;
>  
> @@ -257,6 +258,14 @@ static irqreturn_t dpc_handler(int irq, void *context)
>  		pci_cleanup_aer_uncorrect_error_status(pdev);
>  		pci_aer_clear_fatal_status(pdev);
>  	}
> +}
> +
> +static irqreturn_t dpc_handler(int irq, void *context)
> +{
> +	struct dpc_dev *dpc = context;
> +	struct pci_dev *pdev = dpc->pdev;
> +
> +	dpc_process_error(dpc);
>  
>  	/* We configure DPC so it only triggers on ERR_FATAL */
>  	pcie_do_recovery(pdev, pci_channel_io_frozen, PCIE_PORT_SERVICE_DPC);
> @@ -282,6 +291,25 @@ static irqreturn_t dpc_irq(int irq, void *context)
>  	return IRQ_HANDLED;
>  }
>  
> +void dpc_dev_init(struct pci_dev *pdev, struct dpc_dev *dpc)
> +{

Can you include the kzalloc() here so we don't have to do the alloc in
pci_acpi_add_edr_notifier()?

I think there's also a leak there: pci_acpi_add_edr_notifier()
kzallocs a struct dpc_dev, but I don't see a corresponding kfree().

> +	dpc->cap_pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_DPC);

I think we need to check cap_pos for non-zero here.  It's arguably
safe today because portdrv only calls dpc_probe() when
PCIE_PORT_SERVICE_DPC is set and we only set that if there's a DPC
capability.  But that's a long ways away from here and it's
convoluted, so it's pretty hard to verify that it's safe.

When we add EDR into the picture and call this from
pci_acpi_add_edr_notifier() and edr_handle_event(), I'm pretty sure
it's not safe at all because we have no idea whether the device has a
DPC capability.

Factoring out dpc_dev_init() and the kzalloc() would be a simple
cleanup-type patch all by itself, so it could be separated out for
ease of reviewing.

> +	dpc->pdev = pdev;
> +	pci_read_config_word(pdev, dpc->cap_pos + PCI_EXP_DPC_CAP, &dpc->cap);
> +	pci_read_config_word(pdev, dpc->cap_pos + PCI_EXP_DPC_CTL, &dpc->ctl);
> +
> +	dpc->rp_extensions = (dpc->cap & PCI_EXP_DPC_CAP_RP_EXT);
> +	if (dpc->rp_extensions) {
> +		dpc->rp_log_size =
> +			(dpc->cap & PCI_EXP_DPC_RP_PIO_LOG_SIZE) >> 8;
> +		if (dpc->rp_log_size < 4 || dpc->rp_log_size > 9) {
> +			pci_err(pdev, "RP PIO log size %u is invalid\n",
> +				dpc->rp_log_size);
> +			dpc->rp_log_size = 0;
> +		}
> +	}
> +}
> +
>  #define FLAG(x, y) (((x) & (y)) ? '+' : '-')
>  static int dpc_probe(struct pcie_device *dev)
>  {
> @@ -298,8 +326,8 @@ static int dpc_probe(struct pcie_device *dev)
>  	if (!dpc)
>  		return -ENOMEM;
>  
> -	dpc->cap_pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_DPC);
> -	dpc->pdev = pdev;
> +	dpc_dev_init(pdev, dpc);
> +
>  	set_service_data(dev, dpc);
>  
>  	status = devm_request_threaded_irq(device, dev->irq, dpc_irq,
> @@ -311,18 +339,8 @@ static int dpc_probe(struct pcie_device *dev)
>  		return status;
>  	}
>  
> -	pci_read_config_word(pdev, dpc->cap_pos + PCI_EXP_DPC_CAP, &cap);
> -	pci_read_config_word(pdev, dpc->cap_pos + PCI_EXP_DPC_CTL, &ctl);
> -
> -	dpc->rp_extensions = (cap & PCI_EXP_DPC_CAP_RP_EXT);
> -	if (dpc->rp_extensions) {
> -		dpc->rp_log_size = (cap & PCI_EXP_DPC_RP_PIO_LOG_SIZE) >> 8;
> -		if (dpc->rp_log_size < 4 || dpc->rp_log_size > 9) {
> -			pci_err(pdev, "RP PIO log size %u is invalid\n",
> -				dpc->rp_log_size);
> -			dpc->rp_log_size = 0;
> -		}
> -	}
> +	ctl = dpc->ctl;
> +	cap = dpc->cap;
>  
>  	ctl = (ctl & 0xfff4) | PCI_EXP_DPC_CTL_EN_FATAL | PCI_EXP_DPC_CTL_INT_EN;
>  	pci_write_config_word(pdev, dpc->cap_pos + PCI_EXP_DPC_CTL, ctl);
> diff --git a/drivers/pci/pcie/dpc.h b/drivers/pci/pcie/dpc.h
> new file mode 100644
> index 000000000000..2d82bc917fcb
> --- /dev/null
> +++ b/drivers/pci/pcie/dpc.h
> @@ -0,0 +1,20 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef DRIVERS_PCIE_DPC_H
> +#define DRIVERS_PCIE_DPC_H
> +
> +#include <linux/pci.h>
> +
> +struct dpc_dev {
> +	struct pci_dev		*pdev;
> +	u16			cap_pos;
> +	bool			rp_extensions;
> +	u8			rp_log_size;
> +	u16			ctl;
> +	u16			cap;
> +};
> +
> +pci_ers_result_t dpc_reset_link_common(struct dpc_dev *dpc);
> +void dpc_process_error(struct dpc_dev *dpc);
> +void dpc_dev_init(struct pci_dev *pdev, struct dpc_dev *dpc);
> +
> +#endif /* DRIVERS_PCIE_DPC_H */
> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
> index eefefe03857a..e7b9dfae9035 100644
> --- a/drivers/pci/pcie/err.c
> +++ b/drivers/pci/pcie/err.c
> @@ -162,11 +162,18 @@ static pci_ers_result_t default_reset_link(struct pci_dev *dev)
>  	return rc ? PCI_ERS_RESULT_DISCONNECT : PCI_ERS_RESULT_RECOVERED;
>  }
>  
> -static pci_ers_result_t reset_link(struct pci_dev *dev, u32 service)
> +static pci_ers_result_t reset_link(struct pci_dev *dev, u32 service,
> +				   pci_ers_result_t (*reset_cb)(void *cb_data),
> +				   void *cb_data)

This rejiggering of reset_link() and pcie_do_recovery() is unrelated
to the rest (except that it's needed for EDR, of course), so maybe
could be a separate patch.

We could also consider changing the interface of pcie_do_recovery() to
just add reset_cb and cb_data, and change the existing callers to pass
NULL, NULL.  Then we wouldn't need pcie_do_recovery_common().  I'm not
sure which way would be better.

>  {
>  	pci_ers_result_t status;
>  	struct pcie_port_service_driver *driver = NULL;
>  
> +	if (reset_cb) {
> +		status = reset_cb(cb_data);
> +		goto done;
> +	}
> +
>  	driver = pcie_port_find_service(dev, service);
>  	if (driver && driver->reset_link) {
>  		status = driver->reset_link(dev);
> @@ -178,6 +185,7 @@ static pci_ers_result_t reset_link(struct pci_dev *dev, u32 service)
>  		return PCI_ERS_RESULT_DISCONNECT;
>  	}
>  
> +done:
>  	if (status != PCI_ERS_RESULT_RECOVERED) {
>  		pci_printk(KERN_DEBUG, dev, "link reset at upstream device %s failed\n",
>  			pci_name(dev));
> @@ -187,8 +195,11 @@ static pci_ers_result_t reset_link(struct pci_dev *dev, u32 service)
>  	return status;
>  }
>  
> -void pcie_do_recovery(struct pci_dev *dev, enum pci_channel_state state,
> -		      u32 service)
> +pci_ers_result_t pcie_do_recovery_common(struct pci_dev *dev,
> +				enum pci_channel_state state,
> +				u32 service,
> +				pci_ers_result_t (*reset_cb)(void *cb_data),
> +				void *cb_data)
>  {
>  	pci_ers_result_t status = PCI_ERS_RESULT_CAN_RECOVER;
>  	struct pci_bus *bus;
> @@ -209,7 +220,7 @@ void pcie_do_recovery(struct pci_dev *dev, enum pci_channel_state state,
>  		pci_walk_bus(bus, report_normal_detected, &status);
>  
>  	if (state == pci_channel_io_frozen) {
> -		status = reset_link(dev, service);
> +		status = reset_link(dev, service, reset_cb, cb_data);
>  		if (status != PCI_ERS_RESULT_RECOVERED)
>  			goto failed;
>  	}
> @@ -240,11 +251,20 @@ void pcie_do_recovery(struct pci_dev *dev, enum pci_channel_state state,
>  	pci_aer_clear_device_status(dev);
>  	pci_cleanup_aer_uncorrect_error_status(dev);
>  	pci_info(dev, "device recovery successful\n");
> -	return;
> +
> +	return status;
>  
>  failed:
>  	pci_uevent_ers(dev, PCI_ERS_RESULT_DISCONNECT);
>  
>  	/* TODO: Should kernel panic here? */
>  	pci_info(dev, "device recovery failed\n");
> +
> +	return status;
> +}
> +
> +void pcie_do_recovery(struct pci_dev *dev, enum pci_channel_state state,
> +		      u32 service)
> +{
> +	pcie_do_recovery_common(dev, state, service, NULL, NULL);
>  }
> -- 
> 2.21.0
> 

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