On Wed, Feb 03, 2021 at 10:14:01AM +0800, Mingchuang Qiao wrote:

Hi,

On Mon, 2021-02-01 at 13:32 +0200, Mika Westerberg wrote:

quoted

Hi,

On Fri, Jan 29, 2021 at 03:11:37PM +0800, mingchuang.qiao@mediatek.com wrote:

quoted

From: Mingchuang Qiao <redacted>

In bus scan flow, the "LTR Mechanism Enable" bit of DEVCTL2 register is
configured in pci_configure_ltr(). If device and bridge both support LTR
mechanism, the "LTR Mechanism Enable" bit of device and bridge will be
enabled in DEVCTL2 register. And pci_dev->ltr_path will be set as 1.

If PCIe link goes down when device resets, the "LTR Mechanism Enable" bit
of bridge will change to 0 according to PCIe r5.0, sec 7.5.3.16. However,
the pci_dev->ltr_path value of bridge is still 1.

For following conditions, check and re-configure "LTR Mechanism Enable" bit
of bridge to make "LTR Mechanism Enable" bit mtach ltr_path value.

Typo mtach -> match.

quoted

   -before configuring device's LTR for hot-remove/hot-add
   -before restoring device's DEVCTL2 register when restore device state

Signed-off-by: Mingchuang Qiao <redacted>
---
changes of v2
 -modify patch description
 -reconfigure bridge's LTR before restoring device DEVCTL2 register
changes of v3
 -call pci_reconfigure_bridge_ltr() in probe.c

Hmm, which part of this patch takes care of the reset path? It is not
entirely clear to me at least.

When device resets and link goes down, there seems to have two methods
to recover for software. 
   -One is that trigger device removal and rescan.
   -The other is that restore device with pci_restore_state() after link
comes back up.
For above both scenarios, we need check and reconfigure "LTR Mechanism
Enable" bit of bridge. It's also this patch intends to do.
   -For the rescan scenario, it's done in pci_configure_ltr().
   -For the restore scenario, it's done in pci_restore_pcie_state().

Okay, thanks for the clarification!

_______________________________________________
Linux-mediatek mailing list
Linux-mediatek@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-mediatek