linux-kernel - Re: Serial8250 doesn't populate in /proc/iomem?

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Message-ID: <CAErSpo6uWigsw160BfD1ei0M4hQ+wbK1K4Q37+6+_-+iAV3frg@mail.gmail.com>
Date:	Mon, 10 Dec 2012 19:54:03 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Woody Wu <narkewoody@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	linux-arm <linux-arm-kernel@...ts.infradead.org>,
	linux-samsung-soc@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: Serial8250 doesn't populate in /proc/iomem?

[+cc linux-arm, linux-samsung-soc, linux-serial]

On Sun, Dec 9, 2012 at 11:25 PM, Woody Wu <narkewoody@...il.com> wrote:
> Hi, list
>
> I found some io memory information is lost from /dev/iomem and want to
> find out why.
>
> I have a 2.6.16 kernel running on a ARM board (Samsung S3C2410). From
> the kernel log, I see 16 8250 serial ports were detected, and each of
> thoese ports has a memory address:
>
> Serial: 8250/16550 driver $Revision: 1.90 $ 16 ports, IRQ sharing enabled
> serial8250: tts0 at MMIO 0xe1400000 (irq = 16) is a 16550A
> serial8250: tts1 at MMIO 0xe1400008 (irq = 16) is a 16550A
> serial8250: tts2 at MMIO 0xe1400010 (irq = 17) is a 16550A
> serial8250: tts3 at MMIO 0xe1400018 (irq = 17) is a 16550A
> serial8250: tts4 at MMIO 0xe1400020 (irq = 18) is a 16550A
> serial8250: tts5 at MMIO 0xe1400028 (irq = 18) is a 16550A
> serial8250: tts6 at MMIO 0xe1400030 (irq = 19) is a 16550A
> serial8250: tts7 at MMIO 0xe1400038 (irq = 19) is a 16550A
> serial8250: tts8 at MMIO 0xe1400040 (irq = 48) is a 16550A
> serial8250: tts9 at MMIO 0xe1400048 (irq = 48) is a 16550A
> serial8250: tts10 at MMIO 0xe1400050 (irq = 49) is a 16550A
> serial8250: tts11 at MMIO 0xe1400058 (irq = 49) is a 16550A
> serial8250: tts12 at MMIO 0xe1400060 (irq = 60) is a 16550A
> serial8250: tts13 at MMIO 0xe1400068 (irq = 60) is a 16550A
> serial8250: tts14 at MMIO 0xe1400070 (irq = 61) is a 16550A
> serial8250: tts15 at MMIO 0xe1400078 (irq = 61) is a 16550A
>
> I can read/write these serial ports from /dev/ttys*, in other words,
> they do exist.  I also can find the driver info from /proc/devices:
>
> Character devices:
>
>   ...
>   4 /dev/vc/0
>   4 tty
>   4 tts
>   5 /dev/tty
>   5 /dev/console
>   5 /dev/ptmx
>   7 vcs
>   ...
>
> The problem is, I don't understand why there is no information about
> these ports in /proc/iomem file. The 'iomem' file now contains:
>
> 11000000-11000ffe : AX88796B
> 19000000-19000ffe : AX88796B
> 30000000-33ffffff : System RAM
>   3001c000-301e826b : Kernel text
>   301ea000-302234a3 : Kernel data
> 49000000-490fffff : s3c2410-ohci
>   49000000-490fffff : ohci_hcd
> 4e000000-4e0fffff : s3c2410-nand
>   4e000000-4e0fffff : s3c2410-nand
> 50000000-50003fff : s3c2410-uart.0
>   50000000-500000ff : s3c2410-uart
> 50004000-50007fff : s3c2410-uart.1
>   50004000-500040ff : s3c2410-uart
> 50008000-5000bfff : s3c2410-uart.2
>   50008000-500080ff : s3c2410-uart
> 53000000-530fffff : s3c2410-wdt
> 54000000-540fffff : s3c2410-i2c
> 5a000000-5a0fffff : s3c2410-sdi
>   5a000000-5a0fffff : mmci-s3c2410
>
> You see, there is no serial8250 informations.
>
> Can anyone here please tell me how this can happen?  Does it mean the
> serial8250 driver don't populate or register in the /proc/iomem?

That looks like a bug to me.  There should be entries in /proc/iomem
for the hardware device (showing that something responds at that
address) and for the driver that claims the device.

I think the 8250 core does the reservation in
serial8250_request_std_resource().  You could try putting some printks
in that path to see whether it's exercised.

You're running a fairly old kernel, so it's possible the bug has
already been fixed.

Bjorn
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