From: "Maciej W. Rozycki" <firstname.lastname@example.org>
To: Mikulas Patocka <email@example.com>
Cc: Greg Kroah-Hartman <firstname.lastname@example.org>,
Richard Henderson <email@example.com>,
Ivan Kokshaysky <firstname.lastname@example.org>,
Matt Turner <email@example.com>,
firstname.lastname@example.org, Arnd Bergmann <email@example.com>,
Subject: Re: [PATCH 2/2 v4] alpha: add a delay before serial port read
Date: Sun, 10 May 2020 01:13:43 +0100 (BST) [thread overview]
Message-ID: <alpine.LFD.firstname.lastname@example.org> (raw)
On Thu, 7 May 2020, Mikulas Patocka wrote:
> > > I've created this patch that adds a global macro/variable
> > > serial_port_needs_delay. I've also deleted UPQ_DELAY_BEFORE_READ and test
> > > serial_port_needs_delay directly in io_serial_in, so that the compiler
> > > will optimize it out on non-alpha architectures.
> > That's not good, what about systems with hundreds of serial ports?
> I doubt that someone will conect hundreds of serial ports to such an old
> alpha machine :)
It would be good if PCI serial ports (on add-on cards) were unaffected.
> > > > But, there is no other way to detect this based on hardware
> > > > signatures/types instead? That is usually the best way to do it, right?
> > >
> > > It's hard to detect Alpha without using '#ifdef CONFIG_ALPHA' :) The ISA
> > > serial port hardware is simple, so I think that you can't distinguish it
> > > just based on its behavior.
> > The ISA serial port hardware does not have a unique vendor/product id
> > somewhere? Some other sort of definition that we can use to determine
> > exactly what type of system we are running on?
> AFAIK it doesn't. You can only distinguish 8250, 16550 and 16550A - but
> not the vendor.
You might be able to handle it as a platform device. It's an onboard
peripheral after all and wired permanently subject to further run-time
Otherwise it's a generic off-the-shelf pre-LPC-bus PC Super I/O chip.
Even if we can detect it it'll be there on some x86 machine. And the
issue is a problem that may well be anywhere between the CPU, the
northbridge, the southbridge and the Super I/O, and the weak MMIO ordering
of the Alpha CPU does not help narrowing it down.
Let me see... It's an NS PC87332 piece. For Avanti technical spec see:
for the National Semiconductor piece search for "PC87332.pdf" (no direct
link, but you can download it indirectly):
2.5.8 SuperI/O Identification Register
(SID, Index = 08h)
The SID Register is accessed, like the other configuration
registers, through the Index Register. This read-only register
is used to identify the PC87332 device.
7 6 5 4 3 2 1 0
0 0 0 1 X X X X Super I/O Identification
Index = 08h
I'm not sure how reliable the uniqueness of the four bits in the SID
register is across various PC Super I/O chips. I doubt that the chip has
any observable issues with our serial driver on x86 systems though.
I'm not sure if the situation is fully understood here, but we have a
regression and a working solution now is better than a perfect one in the
unspecified future. We can always improve once we get to the bottom of
I'm in lockdown away from my Alpha machine, but I can try verifying the
solution, also with PCI/e serial ports once I am out of lockdown and back
the right home sometime.
next prev parent reply other threads:[~2020-05-13 22:47 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-06 11:23 [PATCH 2/2] alpha: add a delay before serial port read Mikulas Patocka
2020-05-06 11:47 ` Greg Kroah-Hartman
2020-05-06 15:29 ` [PATCH 2/2 v2] " Mikulas Patocka
2020-05-06 15:49 ` Greg Kroah-Hartman
2020-05-06 15:57 ` Mikulas Patocka
2020-05-06 16:08 ` Greg Kroah-Hartman
2020-05-06 17:04 ` [PATCH 2/2 v3] " Mikulas Patocka
2020-05-06 17:45 ` Greg Kroah-Hartman
2020-05-07 8:18 ` [PATCH 2/2 v4] " Mikulas Patocka
2020-05-07 8:52 ` Greg Kroah-Hartman
2020-05-07 10:53 ` Mikulas Patocka
2020-05-07 11:10 ` Greg Kroah-Hartman
2020-05-07 12:53 ` Mikulas Patocka
2020-05-07 12:57 ` [PATCH 2/2 v5] " Mikulas Patocka
2020-05-07 13:58 ` Greg Kroah-Hartman
2020-05-07 14:03 ` Mikulas Patocka
2020-05-10 0:13 ` Maciej W. Rozycki [this message]
2020-05-23 10:37 ` [PATCH 2/2 v4] " Mikulas Patocka
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