linux-kernel - Re: [PATCH v3 3/7] PCI: Do not disable memory decoding in pci_reassigndev_resource

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Message-Id: <20160701005036.GA18999@gwshan>
Date:	Fri, 1 Jul 2016 10:50:36 +1000
From:	Gavin Shan <gwshan@...ux.vnet.ibm.com>
To:	Yongji Xie <xyjxie@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-doc@...r.kernel.org,
	bhelgaas@...gle.com, alex.williamson@...hat.com, aik@...abs.ru,
	benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
	corbet@....net, warrier@...ux.vnet.ibm.com,
	zhong@...ux.vnet.ibm.com, nikunj@...ux.vnet.ibm.com,
	gwshan@...ux.vnet.ibm.com
Subject: Re: [PATCH v3 3/7] PCI: Do not disable memory decoding in
 pci_reassigndev_resource_alignment()

On Thu, Jun 30, 2016 at 06:53:09PM +0800, Yongji Xie wrote:
>We should not disable memory decoding when we reassign alignment
>in pci_reassigndev_resource_alignment(). It's meaningless and
>have some side effect. For example, some fixup functions such as
>quirk_e100_interrupt() read PCI_COMMAND_MEMORY to know whether
>the devices has been initialized by the firmware or not. If we
>disable memory decoding here, these functions will get a wrong
>information that the devices was not initialized by the firmware
>which may cause a wrong fixup. Besides, disabling memory decoding
>may also break some devices that need to have memory decoding
>always-on during probing.
>

It seems the changelog isn't correct enough if it's talking about
below check in code:

if (!(command & PCI_COMMAND_MEMORY) || !pci_resource_start(dev, 0))
	return;

>Signed-off-by: Yongji Xie <xyjxie@...ux.vnet.ibm.com>
>---
> drivers/pci/pci.c |    8 +-------
> 1 file changed, 1 insertion(+), 7 deletions(-)
>
>diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>index 6ae02de..6241cfc 100644
>--- a/drivers/pci/pci.c
>+++ b/drivers/pci/pci.c
>@@ -4820,7 +4820,6 @@ void pci_reassigndev_resource_alignment(struct pci_dev *dev)
> 	int i;
> 	struct resource *r;
> 	resource_size_t align, size;
>-	u16 command;
>
> 	/* We should never try to reassign VF's alignment */
> 	if (dev->is_virtfn)
>@@ -4838,12 +4837,7 @@ void pci_reassigndev_resource_alignment(struct pci_dev *dev)
> 		return;
> 	}
>
>-	dev_info(&dev->dev,
>-		"Disabling memory decoding and releasing memory resources.\n");
>-	pci_read_config_word(dev, PCI_COMMAND, &command);
>-	command &= ~PCI_COMMAND_MEMORY;
>-	pci_write_config_word(dev, PCI_COMMAND, command);
>-
>+	dev_info(&dev->dev, "Releasing memory resources.\n");

Is there a problem you found with PCI_COMMAND removed? If so, could you
please share more details, thanks.

> 	for (i = 0; i < PCI_BRIDGE_RESOURCES; i++) {
> 		r = &dev->resource[i];
> 		if (!(r->flags & IORESOURCE_MEM))

Thanks,
Gavin