Re: [PATCH 2/2 v2] powerpc/iommu: Remove the dependency on EEH struct in DDW mechanism

[Gavin Shan <gwshan@linux.vnet.ibm.com>]

On Wed, Apr 06, 2016 at 09:20:05PM -0300, Guilherme G. Piccoli wrote:
>Commit 39baadbf36ce ("powerpc/eeh: Remove eeh information from pci_dn")
>changed the pci_dn struct by removing its EEH-related members.
>As part of this clean-up, DDW mechanism was modified to read the device
>configuration address from eeh_dev struct.
>
>As a consequence, now if we disable EEH mechanism on kernel command-line
>for example, the DDW mechanism will fail, generating a kernel oops by
>dereferencing a NULL pointer (which turns to be the eeh_dev pointer).
>
>This patch just changes the configuration address calculation on DDW
>functions to a manual calculation based on pci_dn members instead of
>using eeh_dev-based address.
>
>No functional changes were made. This was tested on pSeries, both
>in PHyp and qemu guest.
>
>Fixes: 39baadbf36ce ("powerpc/eeh: Remove eeh information from pci_dn")
>Signed-off-by: Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>

Reviewed-by: Gavin Shan <gwshan@linux.vnet.ibm.com>

Thanks, Guilherme. Please make sure if it needs to be backported
to stable kernel. I assume it probably needs to be in 3.10+. 

>---
> arch/powerpc/platforms/pseries/iommu.c | 24 ++++++++++++------------
> 1 file changed, 12 insertions(+), 12 deletions(-)
>
>diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
>index bd98ce2..3db2cea 100644
>--- a/arch/powerpc/platforms/pseries/iommu.c
>+++ b/arch/powerpc/platforms/pseries/iommu.c
>@@ -912,7 +912,8 @@ machine_arch_initcall(pseries, find_existing_ddw_windows);
> static int query_ddw(struct pci_dev *dev, const u32 *ddw_avail,
> 			struct ddw_query_response *query)
> {
>-	struct eeh_dev *edev;
>+	struct device_node *dn;
>+	struct pci_dn *pdn;
> 	u32 cfg_addr;
> 	u64 buid;
> 	int ret;
>@@ -923,11 +924,10 @@ static int query_ddw(struct pci_dev *dev, const u32 *ddw_avail,
> 	 * Retrieve them from the pci device, not the node with the
> 	 * dma-window property
> 	 */
>-	edev = pci_dev_to_eeh_dev(dev);
>-	cfg_addr = edev->config_addr;
>-	if (edev->pe_config_addr)
>-		cfg_addr = edev->pe_config_addr;
>-	buid = edev->phb->buid;
>+	dn = pci_device_to_OF_node(dev);
>+	pdn = PCI_DN(dn);
>+	cfg_addr = (pdn->busno << 8) | (pdn->devfn);
>+	buid = pdn->phb->buid;

No parentheses required on the second operand when getting @cfg_addr.
It would be nicer to initialize @buid and then @cfg_addr. When
developers look at the code, they usually check @buid and then
@cfg_addr.

>
> 	ret = rtas_call(ddw_avail[0], 3, 5, (u32 *)query,
> 		  cfg_addr, BUID_HI(buid), BUID_LO(buid));
>@@ -941,7 +941,8 @@ static int create_ddw(struct pci_dev *dev, const u32 *ddw_avail,
> 			struct ddw_create_response *create, int page_shift,
> 			int window_shift)
> {
>-	struct eeh_dev *edev;
>+	struct device_node *dn;
>+	struct pci_dn *pdn;
> 	u32 cfg_addr;
> 	u64 buid;
> 	int ret;
>@@ -952,11 +953,10 @@ static int create_ddw(struct pci_dev *dev, const u32 *ddw_avail,
> 	 * Retrieve them from the pci device, not the node with the
> 	 * dma-window property
> 	 */
>-	edev = pci_dev_to_eeh_dev(dev);
>-	cfg_addr = edev->config_addr;
>-	if (edev->pe_config_addr)
>-		cfg_addr = edev->pe_config_addr;
>-	buid = edev->phb->buid;
>+	dn = pci_device_to_OF_node(dev);
>+	pdn = PCI_DN(dn);
>+	cfg_addr = (pdn->busno << 8) | (pdn->devfn);
>+	buid = pdn->phb->buid;

Same comment as above.

Thanks,
Gavin
>
> 	do {
> 		/* extra outputs are LIOBN and dma-addr (hi, lo) */
>-- 
>2.1.0
>