Re: [PATCH v2] PCI/ATS: Disable ATS when ACS TB is set upstream

[sashiko-bot@kernel.org]

> Enabling ATS allows an endpoint to cache translations and initiate DMA
> requests with Translated addresses, which an upstream bridge with ACS
> Translation Blocking (PCI_ACS_TB) set will block as ACS Violations.
> Because pci_enable_acs() preserves existing PCI_ACS_CTRL bits (e.g., from
> firmware, a kexec kernel, or "pci=config_acs=") without relaxing them,
> PCI_ACS_TB may remain set on upstream bridges.
> 
> Add pci_ats_check_acs() and call it from pci_dma_configure() after
> pci_enable_acs() to walk upstream bridges and clear dev->ats_cap if any
> bridge has PCI_ACS_TB enabled, leaving the endpoint to use Untranslated
> addresses.
> 
> Tested by booting a machine with an endpoint advertising the ATS Capability
> behind a Root Port with PCI_ACS_TB set; verified ATS is disabled and the
> system boots cleanly.
> 
> Signed-off-by: Danny Gonzalez <digonzal@google.com>

Sashiko has reviewed this patch and found no issues.

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