Messages in this thread | | | Subject | Re: [RFC PATCH 3/8] qaic: Create char dev | From | Jeffrey Hugo <> | Date | Thu, 14 May 2020 10:24:44 -0600 |
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On 5/14/2020 9:56 AM, Greg KH wrote: > On Thu, May 14, 2020 at 09:05:30AM -0600, Jeffrey Hugo wrote: >> Wow, thank you for the near immediate response. I'm am quite impressed. >> >> On 5/14/2020 8:12 AM, Greg KH wrote: >>> On Thu, May 14, 2020 at 08:07:41AM -0600, Jeffrey Hugo wrote: >>>> /* Copyright (c) 2019-2020, The Linux Foundation. All rights reserved. */ >>>> +#include <linux/cdev.h> >>>> +#include <linux/idr.h> >>>> +#include <linux/list.h> >>>> +#include <linux/kref.h> >>>> +#include <linux/mhi.h> >>>> #include <linux/module.h> >>>> #include <linux/msi.h> >>>> +#include <linux/mutex.h> >>>> #include <linux/pci.h> >>>> #include <linux/pci_ids.h> >>>> @@ -13,9 +19,242 @@ >>>> #define PCI_DEV_AIC100 0xa100 >>>> #define QAIC_NAME "Qualcomm Cloud AI 100" >>>> +#define QAIC_MAX_MINORS 256 >>> >>> Why have a max? >>> >>> Why not just use a misc device so you make the logic a lot simple, no >>> class or chardev logic to mess with at all. >> >> It was our understanding that the preference is not to add new misc devices. > > Huh, who said that? Not the char/misc maintainer (i.e. me) :) > >> As I go and try to find a supporting reference for that, I cannot find one, >> so I'm not entirely sure where that idea came from. >> >> In addition, we see that the Habana Labs driver also uses chardev, and has >> chosen the same max. We assumed that since their driver is already >> accepted, using the same mechanisms where applicable would be the preferred >> approach. > > They had good reasons why not to use a chardev and convinced me of it. > If you can't come up with them, then stick with a misc for now please.
Interesting. I didn't see any discussion on this.
>> Specific to the max, 256 was chosen as being a factor larger than the >> largest system we have, therefore we figured it wouldn't be hit for a long >> while even as we try to have a look at what might happen down the road. >> Looking at the Habana code, it looks like they have the same value for much >> of the same reasons, although their usecases may vary from ours somewhat. > > Max numbers for no good reason are not a good thing to have. > >> At this time, I don't think we have a strong requirement for a chardev, so >> we could investigate a switch over to a misc dev if you would prefer that >> over following the Habana Labs precedent. All I ask is a confirmation that >> is the approach you would like to see going forward after reviewing the >> above. > > Please use misc.
Ok, will investigate.
-- Jeffrey Hugo Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
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