PCI: pciehp: Clear cmd_busy bit in polling mode

stable inclusion
from stable-v5.10.110
commit 0f56f240157dfeabda945f245dfa75fd5b16a2e3
bugzilla: https://gitee.com/openeuler/kernel/issues/I574AL

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0f56f240157dfeabda945f245dfa75fd5b16a2e3

--------------------------------

commit 92912b17 upstream.

Writes to a Downstream Port's Slot Control register are PCIe hotplug
"commands."  If the Port supports Command Completed events, software must
wait for a command to complete before writing to Slot Control again.

pcie_do_write_cmd() sets ctrl->cmd_busy when it writes to Slot Control.  If
software notification is enabled, i.e., PCI_EXP_SLTCTL_HPIE and
PCI_EXP_SLTCTL_CCIE are set, ctrl->cmd_busy is cleared by pciehp_isr().

But when software notification is disabled, as it is when pcie_init()
powers off an empty slot, pcie_wait_cmd() uses pcie_poll_cmd() to poll for
command completion, and it neglects to clear ctrl->cmd_busy, which leads to
spurious timeouts:

  pcieport 0000:00:03.0: pciehp: Timeout on hotplug command 0x01c0 (issued 2264 msec ago)
  pcieport 0000:00:03.0: pciehp: Timeout on hotplug command 0x05c0 (issued 2288 msec ago)

Clear ctrl->cmd_busy in pcie_poll_cmd() when it detects a Command Completed
event (PCI_EXP_SLTSTA_CC).

[bhelgaas: commit log]
Fixes: a5dd4b4b ("PCI: pciehp: Wait for hotplug command completion where necessary")
Link: https://lore.kernel.org/r/20211111054258.7309-1-zhangliguang@linux.alibaba.com
Link: https://bugzilla.kernel.org/show_bug.cgi?id=215143
Link: https://lore.kernel.org/r/20211126173309.GA12255@wunner.deSigned-off-by: NLiguang Zhang <zhangliguang@linux.alibaba.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Reviewed-by: NLukas Wunner <lukas@wunner.de>
Cc: stable@vger.kernel.org	# v4.19+
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYu Liao <liaoyu15@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/pci/hotplug/pciehp_hpc.c

@@ -93,6 +93,8 @@ static int pcie_poll_cmd(struct controller *ctrl, int timeout)
 		if (slot_status & PCI_EXP_SLTSTA_CC) {
 			pcie_capability_write_word(pdev, PCI_EXP_SLTSTA,
 						   PCI_EXP_SLTSTA_CC);
+			ctrl->cmd_busy = 0;
+			smp_mb();
 			return 1;
 		}
 		msleep(10);