From: Valentine Barshak <vbarshak@ru•mvista.com>
To: Arnd Bergmann <arnd@arndb•de>
Cc: linuxppc-dev@ozlabs•org
Subject: Re: [PATCH] PowerPC: Fix find_legacy_serial_ports on OPB.
Date: Thu, 11 Oct 2007 22:49:32 +0400 [thread overview]
Message-ID: <470E703C.4090301@ru.mvista.com> (raw)
In-Reply-To: <200710111750.41852.arnd@arndb.de>
Arnd Bergmann wrote:
> On Thursday 11 October 2007, Valentine Barshak wrote:
>> Currently find_legacy_serial_ports() can find no serial ports on the OPB.
>> Thus no legacy boot console can be initialized. Just the early udbg console
>> works, which is initialized with udbg_init_44x_as1() on the UART's physical
>> address specified in kernel config. This happens because we look for ns16750
>> and higher serial devices only and expect opb node to have a device type
>> property. This patch makes it look for ns16550 compatible devices and use
>> of_device_is_compatible() for opb instead of checking device type.
>> Lack of legacy serial ports found causes problems for KGDB over serial.
>>
>> Signed-off-by: Valentine Barshak <vbarshak@ru•mvista.com>
>
> The patch would make sense if we were only dealing with flattened device
> tree systems at this point. Unfortunately, IBM is shipping hardware that
> encodes the serial port in exactly the way that find_legacy_serial_ports
> is looking for (parent->type == "opb", compatible = "ns16750" "ns16550"
> "ns16450" i8250").
>
> Changing the search for ns16750 to ns16550 should be fine, but unnecessary
> because AFAIK, all OPB serial imlpementations are actually ns16750 and
> should have that in the device tree as well.
This is a bit odd. The docs say that uart chips on the ppc44x processors
are registry-compatible to 16750, but have 16-byte FIFO's.
This is OK for legacy serial stuff (since it really needs the chip to be
16550-compatible), but the 8250 driver expects 64-byte FIFO size for 16750.
I guess that's why 44x uart dts entries don't have 16750 compatible
property.
>
> For the device type of the bus, please check for both compatible and
> type, so that it still works on machines that are missing the compatible
> property.
>
> Arnd <><
prev parent reply other threads:[~2007-10-11 18:50 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-10-11 15:26 [PATCH] PowerPC: Fix find_legacy_serial_ports on OPB Valentine Barshak
2007-10-11 15:50 ` Arnd Bergmann
2007-10-11 15:53 ` Josh Boyer
2007-10-11 17:09 ` Arnd Bergmann
2007-10-11 19:09 ` [PATCH] PowerPC: Add legacy serial support for OPB with flattened device tree Valentine Barshak
2007-10-11 21:10 ` Arnd Bergmann
2007-10-11 17:26 ` [PATCH] PowerPC: Fix find_legacy_serial_ports on OPB Valentine Barshak
2007-10-11 18:31 ` Josh Boyer
2007-10-12 2:31 ` David Gibson
2007-10-12 11:49 ` Josh Boyer
2007-10-11 18:49 ` Valentine Barshak [this message]
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