Subject: Re: [PATCH V7 04/15] PCI: dwc: Move config space capability search API

From: Bjorn Helgaas <[email-masked]>
Date: Tue, 21 May 2019 16:17:57 -0500

On Fri, May 17, 2019 at 06:08:35PM +0530, Vidya Sagar wrote:
> Move PCIe config space capability search API to common DesignWare file
> as this can be used by both host and ep mode codes.
> 
> Signed-off-by: Vidya Sagar <[email-masked]>
> Acked-by: Gustavo Pimentel <[email-masked]>
> ---
> Changes since [v6]:
> * Exported dw_pcie_find_capability() API
> 
> Changes since [v5]:
> * None
> 
> Changes since [v4]:
> * Removed redundant APIs in pcie-designware-ep.c file after moving them
>   to pcie-designware.c file based on Bjorn's comments.
> 
> Changes since [v3]:
> * Rebased to linux-next top of the tree
> 
> Changes since [v2]:
> * None
> 
> Changes since [v1]:
> * Removed dw_pcie_find_next_ext_capability() API from here and made a
>   separate patch for that
> 
>  .../pci/controller/dwc/pcie-designware-ep.c   | 37 +----------------
>  drivers/pci/controller/dwc/pcie-designware.c  | 40 +++++++++++++++++++
>  drivers/pci/controller/dwc/pcie-designware.h  |  2 +
>  3 files changed, 44 insertions(+), 35 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-ep.c b/drivers/pci/controller/dwc/pcie-designware-ep.c
> index 2bf5a35c0570..65f479250087 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-ep.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
> @@ -40,39 +40,6 @@ void dw_pcie_ep_reset_bar(struct dw_pcie *pci, enum pci_barno bar)
>  	__dw_pcie_ep_reset_bar(pci, bar, 0);
>  }
>  
> -static u8 __dw_pcie_ep_find_next_cap(struct dw_pcie *pci, u8 cap_ptr,
> -			      u8 cap)
> -{
> -	u8 cap_id, next_cap_ptr;
> -	u16 reg;
> -
> -	if (!cap_ptr)
> -		return 0;
> -
> -	reg = dw_pcie_readw_dbi(pci, cap_ptr);
> -	cap_id = (reg & 0x00ff);
> -
> -	if (cap_id > PCI_CAP_ID_MAX)
> -		return 0;
> -
> -	if (cap_id == cap)
> -		return cap_ptr;
> -
> -	next_cap_ptr = (reg & 0xff00) >> 8;
> -	return __dw_pcie_ep_find_next_cap(pci, next_cap_ptr, cap);
> -}
> -
> -static u8 dw_pcie_ep_find_capability(struct dw_pcie *pci, u8 cap)
> -{
> -	u8 next_cap_ptr;
> -	u16 reg;
> -
> -	reg = dw_pcie_readw_dbi(pci, PCI_CAPABILITY_LIST);
> -	next_cap_ptr = (reg & 0x00ff);
> -
> -	return __dw_pcie_ep_find_next_cap(pci, next_cap_ptr, cap);
> -}
> -
>  static int dw_pcie_ep_write_header(struct pci_epc *epc, u8 func_no,
>  				   struct pci_epf_header *hdr)
>  {
> @@ -612,9 +579,9 @@ int dw_pcie_ep_init(struct dw_pcie_ep *ep)
>  		dev_err(dev, "Failed to reserve memory for MSI/MSI-X\n");
>  		return -ENOMEM;
>  	}
> -	ep->msi_cap = dw_pcie_ep_find_capability(pci, PCI_CAP_ID_MSI);
> +	ep->msi_cap = dw_pcie_find_capability(pci, PCI_CAP_ID_MSI);
>  
> -	ep->msix_cap = dw_pcie_ep_find_capability(pci, PCI_CAP_ID_MSIX);
> +	ep->msix_cap = dw_pcie_find_capability(pci, PCI_CAP_ID_MSIX);
>  
>  	offset = dw_pcie_ep_find_ext_capability(pci, PCI_EXT_CAP_ID_REBAR);
>  	if (offset) {
> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> index 83cdd2ce2486..8f53ce63d17e 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.c
> +++ b/drivers/pci/controller/dwc/pcie-designware.c
> @@ -14,6 +14,46 @@
>  
>  #include "pcie-designware.h"
>  
> +/*
> + * These APIs are different from standard pci_find_*capability() APIs in the
> + * sense that former can only be used post device enumeration as they require
> + * 'struct pci_dev *' pointer whereas these APIs require 'struct dw_pcie *'
> + * pointer and can be used before link up also.

I think this comment is slightly misleading because it suggests the
reason we need these DW interfaces is because we're doing something
before a pci_dev pointer is available.

But these DW interfaces are used on devices that will *never* have a
pci_dev pointer because they are not PCI devices.  They're used on
host controller devices, which have a PCIe link on the downstream
side, but the host controller driver operates them using their
upstream, non-PCI interfaces.  Logically, I think they would be
considered parts of Root Complexes, not Root Ports.

There's actually no reason why that upstream interface should look
anything like PCI; it doesn't need to organize registers into
capability lists at all.  It might be convenient for the hardware to
do that and share things with a Root Port device, which *is* a PCI
device, but it's not required.

It also really has nothing to do with whether the link is up.  This
code operates on hardware that is upstream from the link, so we can
reach it regardless of the link.

> + */
> +static u8 __dw_pcie_find_next_cap(struct dw_pcie *pci, u8 cap_ptr,
> +				  u8 cap)
> +{
> +	u8 cap_id, next_cap_ptr;
> +	u16 reg;
> +
> +	if (!cap_ptr)
> +		return 0;
> +
> +	reg = dw_pcie_readw_dbi(pci, cap_ptr);
> +	cap_id = (reg & 0x00ff);
> +
> +	if (cap_id > PCI_CAP_ID_MAX)
> +		return 0;
> +
> +	if (cap_id == cap)
> +		return cap_ptr;
> +
> +	next_cap_ptr = (reg & 0xff00) >> 8;
> +	return __dw_pcie_find_next_cap(pci, next_cap_ptr, cap);
> +}
> +
> +u8 dw_pcie_find_capability(struct dw_pcie *pci, u8 cap)
> +{
> +	u8 next_cap_ptr;
> +	u16 reg;
> +
> +	reg = dw_pcie_readw_dbi(pci, PCI_CAPABILITY_LIST);
> +	next_cap_ptr = (reg & 0x00ff);
> +
> +	return __dw_pcie_find_next_cap(pci, next_cap_ptr, cap);
> +}
> +EXPORT_SYMBOL_GPL(dw_pcie_find_capability);
> +
>  int dw_pcie_read(void __iomem *addr, int size, u32 *val)
>  {
>  	if (!IS_ALIGNED((uintptr_t)addr, size)) {
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index 14762e262758..6cb978132469 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.h
> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -251,6 +251,8 @@ struct dw_pcie {
>  #define to_dw_pcie_from_ep(endpoint)   \
>  		container_of((endpoint), struct dw_pcie, ep)
>  
> +u8 dw_pcie_find_capability(struct dw_pcie *pci, u8 cap);
> +
>  int dw_pcie_read(void __iomem *addr, int size, u32 *val);
>  int dw_pcie_write(void __iomem *addr, int size, u32 val);
>  
> -- 
> 2.17.1
> 

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