linux-kernel - Re: [PATCH v3 1/2] PCI: Add TLP Prefix reading into pcie_read_tlp

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Date: Fri, 3 May 2024 17:53:05 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
	Oliver O'Halloran <oohall@...il.com>,
	Lukas Wunner <lukas@...ner.de>, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v3 1/2] PCI: Add TLP Prefix reading into
 pcie_read_tlp_log()

On Fri, Apr 12, 2024 at 04:36:34PM +0300, Ilpo Järvinen wrote:
> pcie_read_tlp_log() handles only 4 TLP Header Log DWORDs but TLP Prefix
> Log (PCIe r6.1 secs 7.8.4.12 & 7.9.14.13) may also be present.
> 
> Generalize pcie_read_tlp_log() and struct pcie_tlp_log to handle also
> TLP Prefix Log. The layout of relevant registers in AER and DPC
> Capability is not identical because the offsets of TLP Header Log and
> TLP Prefix Log vary so the callers must pass the offsets to
> pcie_read_tlp_log().

I think the layouts of the Header Log and the TLP Prefix Log *are*
identical, but they are at different offsets in the AER Capability vs
the DPC Capability.  Lukas and I have both stumbled over this.

Similar and more comments at:
https://lore.kernel.org/r/20240322193011.GA701027@bhelgaas

> Convert eetlp_prefix_path into integer called eetlp_prefix_max and
> make is available also when CONFIG_PCI_PASID is not configured to
> be able to determine the number of E-E Prefixes.

s/make is/make it/

I think this could be a separate patch.

> --- a/include/linux/aer.h
> +++ b/include/linux/aer.h
> @@ -20,6 +20,7 @@ struct pci_dev;
>  
>  struct pcie_tlp_log {
>  	u32 dw[4];
> +	u32 prefix[4];
>  };
>  
>  struct aer_capability_regs {
> @@ -37,7 +38,9 @@ struct aer_capability_regs {
>  	u16 uncor_err_source;
>  };
>  
> -int pcie_read_tlp_log(struct pci_dev *dev, int where, struct pcie_tlp_log *log);
> +int pcie_read_tlp_log(struct pci_dev *dev, int where, int where2,
> +		      unsigned int tlp_len, struct pcie_tlp_log *log);
> +unsigned int aer_tlp_log_len(struct pci_dev *dev);

I think it was a mistake to expose pcie_read_tlp_log() outside
drivers/pci, and I don't think we should expose aer_tlp_log_len()
either.

We might be stuck with exposing struct pcie_tlp_log since it looks
like ras_event.h uses it.

Bjorn