Re: [PATCH v2] igb_uio: remove out-of-date comment

[Ye Xiaolong <xiaolong.ye@intel.com>]

Hi, Stephen

On 01/17, Ye Xiaolong wrote:
>On 01/16, Stephen Hemminger wrote:
>>On Wed, 16 Jan 2019 15:48:36 +0800
>>Ye Xiaolong <xiaolong.ye@intel.com> wrote:
>>
>>> Hi, Stephen
>>> 
>>> On 01/15, Stephen Hemminger wrote:
>>> >On Wed, 16 Jan 2019 08:34:52 +0800
>>> >Xiaolong Ye <xiaolong.ye@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 The comment for igbuio_pci_irqhandler is out of date as the code evolves,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@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.

Does my above fix make any sense?

Thanks,
Xiaolong
>
>Thanks,
>Xiaolong