Message-ID: <CAErSpo5E4584zgTt4ySPSEFhtwdHDOyrrowirp=SmtmJjDyHgg@mail.gmail.com>
Date:	Mon, 25 Nov 2013 20:33:37 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Chang Liu <cl91tp@...il.com>
Cc:	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Lan Tianyu <tianyu.lan@...el.com>,
	Khalid Aziz <khalid.aziz@...cle.com>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Alan Cox <gnomes@...rguk.ukuu.org.uk>,
	Takao Indoh <indou.takao@...fujitsu.com>,
	Jility <jility09@...il.com>, Florian Otti <f.otti@....at>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PCI: add a quirk for keeping Bus Master bit on shutdown

[+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@...il.com>

I'm not 100% comfortable with disabling bus mastering in general;
see [1] for more details.

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@ldl.usa.hp.com
[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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