[dpdk-dev] [PATCH v2] igb_uio: remove out-of-date comment

[Ye Xiaolong]

On 01/16, Stephen Hemminger wrote:
>On Wed, 16 Jan 2019 15:48:36 +0800
>Ye Xiaolong <xiaolong.ye at intel.com> wrote:
>
>> Hi, Stephen
>> 
>> On 01/15, Stephen Hemminger wrote:
>> >On Wed, 16 Jan 2019 08:34:52 +0800
>> >Xiaolong Ye <xiaolong.ye at intel.com> wrote:
>> >  
>> >> The comment for igbuio_pci_irqhandler is out of date as the code evolves,
>> >> remove it to avoid misleading.
>> >> 
>> >> Signed-off-by: Xiaolong Ye <xiaolong.ye at intel.com>
>> >> ---
>> >>  kernel/linux/igb_uio/igb_uio.c | 4 ----
>> >>  1 file changed, 4 deletions(-)
>> >> 
>> >> diff --git a/kernel/linux/igb_uio/igb_uio.c b/kernel/linux/igb_uio/igb_uio.c
>> >> index 3cf394bdf..d6ac51e79 100644
>> >> --- a/kernel/linux/igb_uio/igb_uio.c
>> >> +++ b/kernel/linux/igb_uio/igb_uio.c
>> >> @@ -185,10 +185,6 @@ igbuio_pci_irqcontrol(struct uio_info *info, s32 irq_state)
>> >>  	return 0;
>> >>  }
>> >>  
>> >> -/**
>> >> - * This is interrupt handler which will check if the interrupt is for the right device.
>> >> - * If yes, disable it here and will be enable later.
>> >> - */
>> >>  static irqreturn_t
>> >>  igbuio_pci_irqhandler(int irq, void *dev_id)
>> >>  {  
>> >
>> >The comment is partially correct; if you look at the legacy case.
>> >
>> >Maybe better to move the comment to pci_check_and_mask_intx in compat.h?
>> >I see there is another incorrect comment there.
>> >  
>> 
>> As I tried to understand pci_check_and_mask_intx behavior, I noticed that it 
>> was introduced by commit 399a3f0d ("igb_uio: fix IRQ mode handling"), and it
>> was derived from igbuio_set_interrupt_mask, however there were two parameters
>> in igbuio_set_interrupt_mask as below:
>> 
>> 	static int
>> 	igbuio_set_interrupt_mask(struct rte_uio_pci_dev *udev, int32_t state)
>> 
>> while the pci_check_and_mask_intx only has 1 parameter,
>> 
>> 	static bool pci_check_and_mask_intx(struct pci_dev *pdev)
>> 
>> but in its function body it still use the "state" accorrding to commit 399a3f0d
>> 
>> +static bool pci_check_and_mask_intx(struct pci_dev *pdev)
>>  {
>> -       /* Some function names changes between 3.2.0 and 3.3.0... */
>> -#if LINUX_VERSION_CODE < KERNEL_VERSION(3, 3, 0)
>> -       pci_unblock_user_cfg_access(pdev);
>> -#else
>> -       pci_cfg_access_unlock(pdev);
>> -#endif
>> +       bool pending;
>> +       uint32_t status;
>> +
>> +       pci_block_user_cfg_access(dev);
>> +       pci_read_config_dword(pdev, PCI_COMMAND, &status);
>> +
>> +       /* interrupt is not ours, goes to out */
>> +       pending = (((status >> 16) & PCI_STATUS_INTERRUPT) != 0);
>> +       if (pending) {
>> +               uint16_t old, new;
>> +
>> +               old = status;
>> +               if (state != 0) <=========================== state still in use
>> +                       new = old & (~PCI_COMMAND_INTX_DISABLE);
>> +               else
>> +                       new = old | PCI_COMMAND_INTX_DISABLE;
>> +
>> +               if (old != new)
>> +                       pci_write_config_word(pdev, PCI_COMMAND, new);
>> +       }
>> +       pci_unblock_user_cfg_access(dev);
>> +
>> +       return pending;
>> 
>> and later this was fixed as a typo in commit 5b2f8137 ("igb_uio: fix typos for 
>> kernel older than 3.3") which seems not correct.
>> 
>>                 old = status;
>> -               if (state != 0)
>> +               if (status != 0)
>> 
>> I feel like that pci_check_and_mask_intx still needs two parameters from code
>> point of view, please correct me if I was wrong or miss anything, or you think 
>> it's sensible, I'll cook a patch for it. 
>> 
>> Thanks,
>> Xiaolong
>
>This code is copy of upstream kernel function, you should look at that.

Thanks, just checked the kernel version of pci_check_and_mask_intx, and it is a 
wrap of pci_check_and_set_intx_mask(pdev, true).


	bool pci_check_and_mask_intx(struct pci_dev *dev)
	{
		return pci_check_and_set_intx_mask(dev, true);
	}


	static bool pci_check_and_set_intx_mask(struct pci_dev *dev, bool mask)
	{
		struct pci_bus *bus = dev->bus;
		...
		origcmd = cmd_status_dword;
		newcmd = origcmd & ~PCI_COMMAND_INTX_DISABLE;
		if (mask)
			newcmd |= PCI_COMMAND_INTX_DISABLE;
		if (newcmd != origcmd)
			bus->ops->write(bus, dev->devfn, PCI_COMMAND, 2, newcmd);

	done:
		raw_spin_unlock_irqrestore(&pci_lock, flags);

		return mask_updated;
	}

if mask is set to ture, PCI_COMMAND_INTX_DISABLE will be set in newcmd.

And current dpdk version doesn't align with it:

	static bool pci_check_and_mask_intx(struct pci_dev *pdev)
	{
		bool pending;
		uint32_t status;

		pci_block_user_cfg_access(pdev);
		pci_read_config_dword(pdev, PCI_COMMAND, &status);

		/* interrupt is not ours, goes to out */
		pending = (((status >> 16) & PCI_STATUS_INTERRUPT) != 0);
		if (pending) {
			uint16_t old, new;

			old = status;
			if (status != 0)
				new = old & (~PCI_COMMAND_INTX_DISABLE);
			else
				new = old | PCI_COMMAND_INTX_DISABLE;

			if (old != new)
				pci_write_config_word(pdev, PCI_COMMAND, new);
		}
		pci_unblock_user_cfg_access(pdev);

		return pending;
	}

In this code, if the interrupt is triggered by this device, both pending and
status will not be 0, so the PCI_COMMAND_INTX_DISABLE will be cleared for new.

To align the behavior with upstream kernel, we may need change like:

diff --git a/kernel/linux/igb_uio/compat.h b/kernel/linux/igb_uio/compat.h
index 8dbb896ae..a78c97f91 100644
--- a/kernel/linux/igb_uio/compat.h
+++ b/kernel/linux/igb_uio/compat.h
@@ -107,10 +107,7 @@ static bool pci_check_and_mask_intx(struct pci_dev *pdev)
                uint16_t old, new;

                old = status;
-               if (status != 0)
-                       new = old & (~PCI_COMMAND_INTX_DISABLE);
-               else
-                       new = old | PCI_COMMAND_INTX_DISABLE;
+               new = old | PCI_COMMAND_INTX_DISABLE;

                if (old != new)
                        pci_write_config_word(pdev, PCI_COMMAND, new);


Please correct me if I was wrong.

Thanks,
Xiaolong