Messages in this thread | | | Subject | Re: [RFC PATCH 3/8] qaic: Create char dev | From | Jeffrey Hugo <> | Date | Sun, 17 May 2020 13:37:20 -0600 |
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On 5/17/2020 1:14 AM, Greg KH wrote: > On Sat, May 16, 2020 at 03:29:19PM -0600, Jeffrey Hugo wrote: >> On 5/16/2020 1:01 AM, Greg KH wrote: >>> On Fri, May 15, 2020 at 03:08:59PM -0600, Jeffrey Hugo wrote: >>>> 2. There are a limited number of dynamic minor numbers for misc devs (64), >>>> so if you are expecting more devices than that, a misc dev is not >>>> appropiate. Also, these minors are shared with other misc dev users, so >>>> depending on the system configuration, you might have significantly less >>>> than 64 minors available for use. >>> >>> I'm pretty sure we can have more than 64 misc devices, that limitation >>> should have been removed a while ago. Try it and see :) >> >> In total, there can be more tha 64 misc devices. However my previous >> comment was specific to dynamic minors (ie devices which do not have an >> assigned minor). The limit on dynamic minors still apears to be 64. Looking >> at the code - >> >> DYNAMIC_MINORS is still 64 >> https://elixir.bootlin.com/linux/v5.7-rc5/source/drivers/char/misc.c#L63 >> >> I see the same in -next >> >> DYNAMIC_MINORS is used to size a bitmap - one bit for each dynamic minor >> misc device that exists at one particular point in time. After all 64 bits >> are consumed by misc_register() by clients requesting a dynamic minor, no >> more dynamic minor misc devices can be registered until some are >> unregistered. >> >> What am I missing? > > Oops, nothing, my fault. We fixed up the allocation of more dynamic > majors for chardev in 2017 and for some reason I thought we also > increased the number of misc dynamic minors at the same time, but that > was incorrect.
No problem.
> I'll gladly take patches that bump up the number of misc minors if > needed.
I don't think its needed at this time, but I will keep that in mind.
> But to get back to the main issue here, you are only going to have 1 or > maybe 2 of these devices in a system at a time, right? So "burning" a > whole major number for that feels like a waste.
Depends on what the customer wants to do. We support a number of systems, but one in particular has the capability of 6-12 devices.
-- Jeffrey Hugo Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
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