On 21-03-04 06:11:43, Bjorn Helgaas wrote: > On Thu, Mar 04, 2021 at 01:40:13PM +0900, Minwoo Im wrote: > > On 21-02-24 23:46:00, Krzysztof Wilczyński wrote: > > > Hi Minwoo, > > > > > > Sorry for a very late reply! > > > > > > [...] > > > > > You might need to improve the subject a little - it should be brief but > > > > > still informative. > > > > > > > > > > > __pci_set_mater() has debug log in there so that it would be better to > > > > > > take this function. So take __pci_set_master() function rather than > > > > > > open coding it. This patch didn't move __pci_set_master() to above to > > > > > > avoid churns. > > > > > [...] > > > > > > > > > > It would be __pci_set_master() in the sentence above. Also, perhaps > > > > > "use" would be better than "take". Generally, this commit message might > > > > > need a little improvement to be more clear why are you do doing this. > > > > > > > > Sure, if we consolidate bus master enable clear functions to a single > > > > one, it would be better to debug and tracing the kernel behaviors. > > > > > > > > Let me describe this 'why' to the description. > > > > > > Sounds great! Thank you! > > > > > > [...] > > > > > You could use pci_clear_master(), which we export and that internally > > > > > calls __pci_set_master(), so there would be no need to add any forward > > > > > declarations or to move anything around in the file. > > > > > > > > Moving delcaration to above might be churn, and I agree with your point. > > > > > > I am sure that when it makes sense, then probably folks would not > > > object, especially since "churn" can be subjective. > > > > > > > > Having said that, there is a difference between do_pci_disable_device() > > > > > and how __pci_set_master() works - the latter sets the is_busmaster flag > > > > > accordingly on the given device whereas the former does not. This might > > > > > be of some significance - not sure if we should or should not set this, > > > > > since the do_pci_disable_device() does not do that (perhaps it's on > > > > > purpose or due to some hisoric reasons). > > > > > > > > Thanks for pointing out this. I think the difference about > > > > `is_busmaster` flag looks like it should not be cleared in case of power > > > > suspend case: > > > > > > > > # Suspend > > > > pci_pm_default_suspend() > > > > pci_disable_enabled_device() > > > > > > > > # Resume > > > > pci_pm_reenable_device() > > > > pci_set_master() <-- This is based on (is_busmaster) > > > > > > > > > > > > Please let me know if I'm missing here, and appreciate pointing that > > > > out. Maybe I can post v2 patch with add an argument of whether > > > > `is_busmaster` shoud be set inside of the function or not to > > > > __pci_set_master()? > > > [...] > > > > > > Nothing is ever simple, isn't it? :-) > > > > > > We definitely need to make sure that PM can keep relying on the > > > is_busmaster flag to restore bus mastering to previous state after the > > > device would resume after being suspended. > > > > Yes, > > > > > If we add another boolean argument, then we would need to update the > > > __pci_set_master() only in two other places, aside of using it in the > > > do_pci_disable_device() function, as per (as of 5.11.1 kernel): > > > > I agree with this approach. I can try it by adding another bool > > argument to decide whether to update the is_busmaster flag or not inside > > of the __pci_set_master. > > > > > > > > File Line Content > > > drivers/pci/pci.c 4308 __pci_set_master(dev, true); > > > drivers/pci/pci.c 4319 __pci_set_master(dev, false); > > > > > > This is not all that terrible, provided that we _really_ do want to > > > change this function signature and then add another condition inside. > > > > > > What do you think? If you still like the idea, then send second version > > > over with all the other proposed changes. > > > > Let me prepare the next version of this patch. Thanks! > > Can you clarify what the purpose of this patch is? Is it to fix a > defect, improve debug output, make the code cleaner, etc? > > The commit log really just describes *what* the patch does, and I'm > looking for the *why*. I should have described why this patch is introdcued. do_pci_disable_device clears the Bus Master Enable bit just like what __pci_set_master does which is kind of duplications. Also, __pci_set_master has debug print log which is useful for users to figure out whether bus master is set or cleared. This patch makes do_pci_disable_device call __pci_set_master to take the debug log advantages and make code cleaner by clearing duplicated codes. > Bjorn
