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Message-ID: <4c6d6b57-d868-eccb-7cfb-66008af530bb@ti.com>
Date: Wed, 22 Sep 2021 06:56:09 +0530
From: Kishon Vijay Abraham I <kishon@...com>
To: Marc Zyngier <maz@...nel.org>
CC: Thomas Gleixner <tglx@...utronix.de>,
Bjorn Helgaas <bhelgaas@...gle.com>,
<linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
<lokeshvutla@...com>
Subject: Re: [PATCH 1/3] PCI: Add support in pci_walk_bus() to invoke callback
matching RID
Hi Marc,
On 20/09/21 11:31 pm, Marc Zyngier wrote:
> On Mon, 20 Sep 2021 15:28:52 +0100,
> Kishon Vijay Abraham I <kishon@...com> wrote:
>>
>> Hi Marc,
>>
>> On 20/09/21 2:26 pm, Marc Zyngier wrote:
>>> On Mon, 20 Sep 2021 07:41:31 +0100,
>>> Kishon Vijay Abraham I <kishon@...com> wrote:
>>>>
>>>> Add two arguments to pci_walk_bus() [requestorID and mask], and add
>>>> support in pci_walk_bus() to invoke the *callback* only for devices
>>>> whose RequestorID after applying *mask* matches with *requestorID*
>>>> passed as argument.
>>>>
>>>> This is done in preparation for calculating the total number of
>>>> interrupt vectors that has to be supported by a specific GIC ITS device ID,
>>>> specifically when "msi-map-mask" is populated in device tree.
>>>>
>>>> Signed-off-by: Kishon Vijay Abraham I <kishon@...com>
>>>> ---
>>>> drivers/pci/bus.c | 13 +++++++++----
>>>> include/linux/pci.h | 7 +++++--
>>>> 2 files changed, 14 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
>>>> index 3cef835b375f..e381e639ceaa 100644
>>>> --- a/drivers/pci/bus.c
>>>> +++ b/drivers/pci/bus.c
>>>> @@ -358,10 +358,12 @@ void pci_bus_add_devices(const struct pci_bus *bus)
>>>> }
>>>> EXPORT_SYMBOL(pci_bus_add_devices);
>>>>
>>>> -/** pci_walk_bus - walk devices on/under bus, calling callback.
>>>> +/** __pci_walk_bus - walk devices on/under bus matching requestor ID, calling callback.
>>>> * @top bus whose devices should be walked
>>>> * @cb callback to be called for each device found
>>>> * @userdata arbitrary pointer to be passed to callback.
>>>> + * @rid Requestor ID that has to be matched for the callback to be invoked
>>>> + * @mask Mask that has to be applied to pci_dev_id(), before compating it with @rid
>>>> *
>>>> * Walk the given bus, including any bridged devices
>>>> * on buses under this bus. Call the provided callback
>>>> @@ -371,8 +373,8 @@ EXPORT_SYMBOL(pci_bus_add_devices);
>>>> * other than 0, we break out.
>>>> *
>>>> */
>>>> -void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
>>>> - void *userdata)
>>>> +void __pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
>>>> + void *userdata, u32 rid, u32 mask)
>>>> {
>>>> struct pci_dev *dev;
>>>> struct pci_bus *bus;
>>>> @@ -399,13 +401,16 @@ void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
>>>> } else
>>>> next = dev->bus_list.next;
>>>>
>>>> + if (mask != 0xffff && ((pci_dev_id(dev) & mask) != rid))
>>>
>>> Why the check for the mask? I also wonder whether the mask should apply
>>> to the rid as well:
>>
>> If the mask is set for all 16bits, then there is not going to be two PCIe
>> devices which gets the same ITS device ID right? So no need for calculating
>> total number of vectors?
>
> Are we really arguing about the cost of a compare+branch vs some
> readability? Or is there an actual correctness issue here?
It is for correctness. So existing pci_walk_bus() doesn't invoke cb based on
rid. So when we convert to __pci_walk_bus(), existing callers of pci_walk_bus()
might not invoke cb for some devices without the check.
>
>>>
>>> if ((pci_dev_id(dev) & mask) != (rid & mask))
>
> Because I think the above expression is a lot more readable (and
> likely more correct) than what you are suggesting.
That would result in existing pci_walk_bus() behave differently from what was
before this patch no?
I'm having something like this below
+#define pci_walk_bus(top, cb, userdata) \
+ __pci_walk_bus((top), (cb), (userdata), 0x0, 0xffff)
So if we add only "if ((pci_dev_id(dev) & mask) != (rid & mask))", the callback
will not be invoked for any devices (other than one with rid = 0)
>
>>>
>>>> + continue;
>>>> +
>>>> retval = cb(dev, userdata);
>>>> if (retval)
>>>> break;
>>>> }
>>>> up_read(&pci_bus_sem);
>>>> }
>>>> -EXPORT_SYMBOL_GPL(pci_walk_bus);
>>>> +EXPORT_SYMBOL_GPL(__pci_walk_bus);
>>>>
>>>> struct pci_bus *pci_bus_get(struct pci_bus *bus)
>>>> {
>>>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>>>> index cd8aa6fce204..8500fec56e50 100644
>>>> --- a/include/linux/pci.h
>>>> +++ b/include/linux/pci.h
>>>> @@ -1473,14 +1473,17 @@ const struct pci_device_id *pci_match_id(const struct pci_device_id *ids,
>>>> int pci_scan_bridge(struct pci_bus *bus, struct pci_dev *dev, int max,
>>>> int pass);
>>>>
>>>> -void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
>>>> - void *userdata);
>>>> +void __pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
>>>> + void *userdata, u32 rid, u32 mask);
>>>> int pci_cfg_space_size(struct pci_dev *dev);
>>>> unsigned char pci_bus_max_busnr(struct pci_bus *bus);
>>>> void pci_setup_bridge(struct pci_bus *bus);
>>>> resource_size_t pcibios_window_alignment(struct pci_bus *bus,
>>>> unsigned long type);
>>>>
>>>> +#define pci_walk_bus(top, cb, userdata) \
>>>> + __pci_walk_bus((top), (cb), (userdata), 0x0, 0xffff)
>>>
>>> Please keep this close to the helper it replaces. I also really
>>> dislike the use of this raw 0xffff. Don't we already have a named
>>> constant that represents the mask for a RID?
>>
>> I didn't find one on quick look but let me check.
>
> Worse case, you could create your own.
sure.
Thanks,
Kishon
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