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Bug#1015871: Please enable CONFIG_PCI_P2PDMA



Hello,

On Fri, Jul 22, 2022 at 10:06:54PM +0200, Simon Richter wrote:
> would it be possible to enable this option to allow PCIe devices to do
> direct data transfers?

Enabling it for amd64 and ppc64el would be done by the following change:

diff --git a/debian/config/amd64/config b/debian/config/amd64/config
index 42ac252164f1..c4b37af83061 100644
--- a/debian/config/amd64/config
+++ b/debian/config/amd64/config
@@ -194,6 +194,7 @@ CONFIG_NVDIMM_PFN=y
 ##
 ## file: drivers/pci/Kconfig
 ##
+CONFIG_PCI_P2PDMA=y
 CONFIG_PCI_HYPERV=y
 
 ##
diff --git a/debian/config/kernelarch-powerpc/config-arch-64-le b/debian/config/kernelarch-powerpc/config-arch-64-le
index 14a2e754d39e..d0503b3e17f6 100644
--- a/debian/config/kernelarch-powerpc/config-arch-64-le
+++ b/debian/config/kernelarch-powerpc/config-arch-64-le
@@ -28,6 +28,11 @@ CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND=y
 ##
 CONFIG_CXL_BUS=y
 
+##
+## file: drivers/pci/Kconfig
+##
+CONFIG_PCI_P2PDMA=y
+
 ##
 ## file: drivers/pcmcia/Kconfig
 ##
@@ -38,3 +43,8 @@ CONFIG_CXL_BUS=y
 ##
 #. See #789070
 # CONFIG_HIBERNATION is not set
+
+##
+## file: mm/Kconfig
+##
+CONFIG_ZONE_DEVICE=y

ZONE_DEVICE is a direct dependency of PCI_P2PDMA that isn't currently
enabled on ppc64el.

I hesitate to actually enable it because I don't understand PCI good
enough to judge it's a safe choice for the Debian kernel. Also I wonder
about "If unsure, say N" in the Kconfig help text. Is this only because
people who benefit from this setting are expected to be sure?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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