From: Jeffrey Hugo <jhugo@codeaurora.org>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: arnd@arndb.de, manivannan.sadhasivam@linaro.org,
bjorn.andersson@linaro.org, wufan@codeaurora.org,
pratanan@codeaurora.org, linux-arm-msm@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 3/8] qaic: Create char dev
Date: Sun, 17 May 2020 13:37:20 -0600 [thread overview]
Message-ID: <46581ccf-9cd4-3b9f-9b03-ed1264dac03b@codeaurora.org> (raw)
In-Reply-To: <20200517071417.GA3090070@kroah.com>
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.
next prev parent reply other threads:[~2020-05-17 19:37 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-14 14:07 [RFC PATCH 0/8] Qualcomm Cloud AI 100 driver Jeffrey Hugo
2020-05-14 14:07 ` [RFC PATCH 1/8] qaic: Add skeleton driver Jeffrey Hugo
2020-05-15 0:43 ` Jeffrey Hugo
2020-05-15 6:37 ` Greg KH
2020-05-14 14:07 ` [RFC PATCH 2/8] qaic: Add and init a basic mhi controller Jeffrey Hugo
2020-05-14 14:07 ` [RFC PATCH 3/8] qaic: Create char dev Jeffrey Hugo
2020-05-14 14:12 ` Greg KH
2020-05-14 15:05 ` Jeffrey Hugo
2020-05-14 15:56 ` Greg KH
2020-05-14 16:24 ` Jeffrey Hugo
2020-05-15 21:08 ` Jeffrey Hugo
2020-05-16 7:01 ` Greg KH
2020-05-16 21:29 ` Jeffrey Hugo
2020-05-17 7:14 ` Greg KH
2020-05-17 19:37 ` Jeffrey Hugo [this message]
2020-05-14 14:07 ` [RFC PATCH 4/8] qaic: Implement control path Jeffrey Hugo
2020-05-14 14:07 ` [RFC PATCH 5/8] qaic: Implement data path Jeffrey Hugo
2020-05-14 14:14 ` Greg KH
2020-05-14 15:06 ` Jeffrey Hugo
2020-05-14 15:56 ` Greg KH
2020-05-14 16:12 ` Jeffrey Hugo
2020-05-14 16:37 ` Greg KH
2020-05-14 16:45 ` Jeffrey Hugo
2020-05-14 21:36 ` Arnd Bergmann
2020-05-14 22:06 ` Jeffrey Hugo
2020-05-14 22:20 ` Arnd Bergmann
2020-05-14 14:07 ` [RFC PATCH 6/8] qaic: Implement PCI link status error handlers Jeffrey Hugo
2020-05-14 14:07 ` [RFC PATCH 7/8] qaic: Implement MHI error status handler Jeffrey Hugo
2020-05-14 14:07 ` [RFC PATCH 8/8] MAINTAINERS: Add entry for QAIC driver Jeffrey Hugo
2020-05-19 5:08 ` [RFC PATCH 0/8] Qualcomm Cloud AI 100 driver Dave Airlie
2020-05-19 14:57 ` Jeffrey Hugo
2020-05-19 17:41 ` Greg Kroah-Hartman
2020-05-19 18:07 ` Jeffrey Hugo
2020-05-19 18:12 ` Greg Kroah-Hartman
2020-05-19 18:26 ` Jeffrey Hugo
2020-05-20 5:32 ` Greg Kroah-Hartman
2020-05-19 17:33 ` Greg Kroah-Hartman
2020-05-19 6:57 ` Manivannan Sadhasivam
2020-05-19 14:16 ` Jeffrey Hugo
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