Subject: Re: [PATCH V2 3/9] PCI/TPH: Implement a command line option to disable TPH

From: Jonathan Cameron <[email-masked]>
Date: Fri, 7 Jun 2024 17:27:01 +0100

On Fri, 31 May 2024 16:38:35 -0500
Wei Huang <[email-masked]> wrote:

> Provide a kernel option, with related helper functions, to completely
> disable TPH so that no TPH headers are generated.

Why would someone use this option?

> 
> Co-developed-by: Eric Van Tassell <[email-masked]>
> Signed-off-by: Eric Van Tassell <[email-masked]>
> Signed-off-by: Wei Huang <[email-masked]>
> Reviewed-by: Ajit Khaparde <[email-masked]>
> Reviewed-by: Somnath Kotur <[email-masked]> 
> Reviewed-by: Andy Gospodarek <[email-masked]>
> ---
>  .../admin-guide/kernel-parameters.txt         |  1 +
>  drivers/pci/pci-driver.c                      |  7 ++++-
>  drivers/pci/pci.c                             | 12 ++++++++
>  drivers/pci/pcie/tph.c                        | 30 +++++++++++++++++++
>  include/linux/pci-tph.h                       | 19 ++++++++++++
>  include/linux/pci.h                           |  1 +
>  6 files changed, 69 insertions(+), 1 deletion(-)
>  create mode 100644 include/linux/pci-tph.h
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 500cfa776225..fedcc69e35c1 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -4623,6 +4623,7 @@
>  		nomio		[S390] Do not use MIO instructions.
>  		norid		[S390] ignore the RID field and force use of
>  				one PCI domain per PCI function
> +		notph		[PCIE] Do not use PCIe TPH
>  
>  	pcie_aspm=	[PCIE] Forcibly enable or ignore PCIe Active State Power
>  			Management.
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index af2996d0d17f..9722d070c0ca 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -21,6 +21,7 @@
>  #include <linux/acpi.h>
>  #include <linux/dma-map-ops.h>
>  #include <linux/iommu.h>
> +#include <linux/pci-tph.h>
>  #include "pci.h"
>  #include "pcie/portdrv.h"
>  
> @@ -322,8 +323,12 @@ static long local_pci_probe(void *_ddi)
>  	pm_runtime_get_sync(dev);
>  	pci_dev->driver = pci_drv;
>  	rc = pci_drv->probe(pci_dev, ddi->id);
> -	if (!rc)
> +	if (!rc) {
> +		if (pci_tph_disabled())
> +			pcie_tph_disable(pci_dev);
> +
>  		return rc;
> +	}
>  	if (rc < 0) {
>  		pci_dev->driver = NULL;
>  		pm_runtime_put_sync(dev);
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 59e0949fb079..31c443504ce9 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -157,6 +157,9 @@ static bool pcie_ari_disabled;
>  /* If set, the PCIe ATS capability will not be used. */
>  static bool pcie_ats_disabled;
>  
> +/* If set, the PCIe TPH capability will not be used. */
> +static bool pcie_tph_disabled;
> +
>  /* If set, the PCI config space of each device is printed during boot. */
>  bool pci_early_dump;
>  
> @@ -166,6 +169,12 @@ bool pci_ats_disabled(void)
>  }
>  EXPORT_SYMBOL_GPL(pci_ats_disabled);
>  
> +bool pci_tph_disabled(void)
> +{
> +	return pcie_tph_disabled;
> +}
> +EXPORT_SYMBOL_GPL(pci_tph_disabled);
> +
>  /* Disable bridge_d3 for all PCIe ports */
>  static bool pci_bridge_d3_disable;
>  /* Force bridge_d3 for all PCIe ports */
> @@ -6806,6 +6815,9 @@ static int __init pci_setup(char *str)
>  				pci_no_domains();
>  			} else if (!strncmp(str, "noari", 5)) {
>  				pcie_ari_disabled = true;
> +			} else if (!strcmp(str, "notph")) {
> +				pr_info("PCIe: TPH is disabled\n");
> +				pcie_tph_disabled = true;
>  			} else if (!strncmp(str, "cbiosize=", 9)) {
>  				pci_cardbus_io_size = memparse(str + 9, &str);
>  			} else if (!strncmp(str, "cbmemsize=", 10)) {
> diff --git a/drivers/pci/pcie/tph.c b/drivers/pci/pcie/tph.c
> index 5f0cc06b74bb..5dc533b89a33 100644
> --- a/drivers/pci/pcie/tph.c
> +++ b/drivers/pci/pcie/tph.c
> @@ -16,11 +16,41 @@
>  #include <linux/errno.h>
>  #include <linux/msi.h>
>  #include <linux/pci.h>
> +#include <linux/pci-tph.h>
>  #include <linux/msi.h>
>  #include <linux/pci-acpi.h>
>  
>  #include "../pci.h"
>  
> +static int tph_set_reg_field_u32(struct pci_dev *dev, u8 offset, u32 mask,
> +				 u8 shift, u32 field)

I'm unconvinced this helper makes sense.  Do we do similar for other
PCI capabilities?

If it does make sense to have a field update, then provide
one alongside pci_read_config_dword() etc.

> +{
> +	u32 reg_val;
> +	int ret;
> +
> +	if (!dev->tph_cap)
> +		return -EINVAL;
> +
> +	ret = pci_read_config_dword(dev, dev->tph_cap + offset, &reg_val);
> +	if (ret)
> +		return ret;
> +
> +	reg_val &= ~mask;
> +	reg_val |= (field << shift) & mask;
> +
> +	ret = pci_write_config_dword(dev, dev->tph_cap + offset, reg_val);
> +
> +	return ret;

	return pci_write_config_dword();

> +}
> +
> +int pcie_tph_disable(struct pci_dev *dev)
> +{
> +	return  tph_set_reg_field_u32(dev, PCI_TPH_CTRL,

extra space after return

> +				      PCI_TPH_CTRL_REQ_EN_MASK,
> +				      PCI_TPH_CTRL_REQ_EN_SHIFT,
> +				      PCI_TPH_REQ_DISABLE);
> +}
> +
>  void pcie_tph_init(struct pci_dev *dev)
>  {
>  	dev->tph_cap = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_TPH);