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. > 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. That is, if you even need a character device node :) thanks, greg k-h
