On Tue, Jan 28, 2025 at 08:00:39PM +0200, Ilpo Järvinen wrote:
On Tue, 28 Jan 2025, Sasha Levin wrote:From: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx> [ Upstream commit e5321ae10e1323359a5067a26dfe98b5f44cc5e6 ] eetlp_prefix_path in the struct pci_dev tells if End-End TLP Prefixes are supported by the path or not, and the value is only calculated if CONFIG_PCI_PASID is set. The Max End-End TLP Prefixes field in the Device Capabilities Register 2 also tells how many (1-4) End-End TLP Prefixes are supported (PCIe r6.2 sec 7.5.3.15). The number of supported End-End Prefixes is useful for reading correct number of DWORDs from TLP Prefix Log register in AER capability (PCIe r6.2 sec 7.8.4.12). Replace eetlp_prefix_path with eetlp_prefix_max and determine the number of supported End-End Prefixes regardless of CONFIG_PCI_PASID so that an upcoming commit generalizing TLP Prefix Log register reading does not have to read extra DWORDs for End-End Prefixes that never will be there. The value stored into eetlp_prefix_max is directly derived from device's Max End-End TLP Prefixes and does not consider limitations imposed by bridges or the Root Port beyond supported/not supported flags. This is intentional for two reasons: 1) PCIe r6.2 spec sections 2.2.10.4 & 6.2.4.4 indicate that a TLP is malformed only if the number of prefixes exceed the number of Max End-End TLP Prefixes, which seems to be the case even if the device could never receive that many prefixes due to smaller maximum imposed by a bridge or the Root Port. If TLP parsing is later added, this distinction is significant in interpreting what is logged by the TLP Prefix Log registers and the value matching to the Malformed TLP threshold is going to be more useful. 2) TLP Prefix handling happens autonomously on a low layer and the value in eetlp_prefix_max is not programmed anywhere by the kernel (i.e., there is no limiter OS can control to prevent sending more than N TLP Prefixes). Link: https://lore.kernel.org/r/20250114170840.1633-7-ilpo.jarvinen@xxxxxxxxxxxxxxx Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx> Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> Reviewed-by: Yazen Ghannam <yazen.ghannam@xxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>Hi, Why is this being auto selected? It's not a fix nor do I see any dependency related tags. Unless the entire TLP consolidation would be going into stable, I don't see much value for this change in stable kernels.
I wasn't too sure about it either. My thinking was that there is a spec compatibility issue here, but looks like I was wrong. I'll drop it, thanks! -- Thanks, Sasha
