Re: [PATCH] PCI: add a quirk for keeping Bus Master bit on shutdown
From: Khalid Aziz
Date: Tue Nov 26 2013 - 11:41:42 EST
On 11/25/2013 08:33 PM, Bjorn Helgaas wrote:
[+cc Lan, Khalid, Konstantin, Alan, Takao, Jility, Florian, linux-kernel]
On Tue, Nov 12, 2013 at 07:40:03PM +0000, Chang Liu wrote:
This fixes https://bugzilla.kernel.org/show_bug.cgi?id=63861
Commit b566a22c2 and 7897e60227 made pci_device_shutdown()
unconditionally clear Bus Master bit for every pci devices.
While this works for most hardware, certain devices are not
compatible with this. Intel Lynx Point-LP SATA Controller,
for example, will hang the system if its Bus Master bit is
cleared during device shutdown. This patch adds a pci quirk
so that device drivers can instruct pci_device_shutdown()
to keep Bus Master from being cleared, and then implements
this mechanism for the Intel Lynx Point-LP AHCI driver.
Signed-off-by: Chang Liu <cl91tp@xxxxxxxxx>
I'm not 100% comfortable with disabling bus mastering in general;
see [1] for more details.
Disabling Bus Master bit is effectively a brute force and not an elegant
way to stop unwanted DMA. It can have side effects as Alan and others
pointed out in the original discussion, and we are now seeing one with
Lynx Point on Acer. Eric had pointed out in original discussion -
<http://marc.info/?l=linux-pci&m=133901193430829&w=2> that this code
change moves failure from a random point in the kexec'd kernel to a
predictable point on shutdown path where it becomes lot easier to debug
than a random memory overwrite. For kexec and kdump to be successful,
all devices need to be shut down cleanly and be in a state where they
can be reinitialized by the kexec'd kernel. Either device drivers do it
or we forcibly stop all DMAs by clearing Bus Master bit. If we stop
clearing Bus Master bit on shutdown, we will resurrect the old issue of
random memory corruption on kexec.
Regular shutdown being affected by Bus Master bit being cleared is not a
comfortable situation. Would it be better if we clear Bus Master bit
only if devices are being shut down in preparation for kexec?
Patch proposed by Chang Liu is similar to the approach I had suggested
in discussions last year -
<http://marc.info/?l=linux-pci&m=133900414027717&w=2> where driver tells
the PCI subsystem if it is not ok with Bus Master bit being cleared and
I can accept this approach. Every time we come across a broken
driver/device that implodes on Bus Master bit being cleared, we add
"pdev->keep_busmaster_on_shutdown = 1;" to the driver. This will be an
ongoing process.
--
Khalid
But given that we have been doing it for quite a while (b566a22c2 appeared
in v3.5 on Jul 21, 2012), and Lynx Point should be in lots of machines, I'm
surprised that we don't see more reports of this problem if it really
affects all Lynx Point parts.
Jility reported the same problem [2], and I did find one other similar
report [3] from Florian. All three reports (Chang, Jility, Florian) are on
the same exact machine (Acer V5-573G), which seems sort of suspicious.
Lan, do you have access to any Lynx Point boxes? Can you test and see
whether they hang on power-off also? I suspect this might be something
specific to the Acer box, not a generic Lynx Point issue.
Bjorn
[1] http://lkml.kernel.org/r/20120427190033.GA17588@xxxxxxxxxxxxxx
[2] https://bugzilla.kernel.org/show_bug.cgi?id=63861#c21
[3] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1249329
---
As per Takao's suggestion, add a new member into struct pci_dev
and add a quirk in the ahci driver. I tested this on my
machine (Acer V5-573G) and it works fine.
drivers/ata/ahci.c | 8 ++++++++
drivers/pci/pci-driver.c | 11 ++++++++---
include/linux/pci.h | 1 +
3 files changed, 17 insertions(+), 3 deletions(-)
diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
index 8e28f92..de6efcb 100644
--- a/drivers/ata/ahci.c
+++ b/drivers/ata/ahci.c
@@ -1385,6 +1385,14 @@ static int ahci_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
pci_set_master(pdev);
+ /* We normally clear Bus Master on pci device shutdown. However,
+ * doing so for Intel Lynx Point-LP SATA Controller [AHCI mode]
+ * hangs the system. Therefore keep it.
+ * See bug report: https://bugzilla.kernel.org/show_bug.cgi?id=63861
+ */
+ if (pdev->vendor == PCI_VENDOR_ID_INTEL && pdev->device == 0x9c03)
+ pdev->keep_busmaster_on_shutdown = 1;
+
if (hpriv->flags & AHCI_HFLAG_MULTI_MSI)
return ahci_host_activate(host, pdev->irq, n_msis);
diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index 38f3c01..ff15b0c 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -392,10 +392,15 @@ static void pci_device_shutdown(struct device *dev)
pci_msix_shutdown(pci_dev);
/*
- * Turn off Bus Master bit on the device to tell it to not
- * continue to do DMA. Don't touch devices in D3cold or unknown states.
+ * If the hardware is okay with it, turn off Bus Master bit
+ * on the device to tell it not to continue doing DMA.
+ * Don't touch devices in D3cold or unknown states.
+ * On certain hardware clearing Bus Master bit on shutdown
+ * may hang the entire system. In these cases the driver of
+ * these devices should set keep_busmaster_on_shutdown to 1.
*/
- if (pci_dev->current_state <= PCI_D3hot)
+ if (!pci_dev->keep_busmaster_on_shutdown
+ && pci_dev->current_state <= PCI_D3hot)
pci_clear_master(pci_dev);
}
diff --git a/include/linux/pci.h b/include/linux/pci.h
index da172f9..63db735 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -322,6 +322,7 @@ struct pci_dev {
/* keep track of device state */
unsigned int is_added:1;
unsigned int is_busmaster:1; /* device is busmaster */
+ unsigned int keep_busmaster_on_shutdown:1; /* do not clear busmaster on shutdown */
unsigned int no_msi:1; /* device may not use msi */
unsigned int block_cfg_access:1; /* config space access is blocked */
unsigned int broken_parity_status:1; /* Device generates false positive parity */
--
1.8.4.2
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