RE: [PATCH] PCI serial card support

[Dugger, Donald D]

To my knowledge there is no way to query the device to discover this.  You can 
create an internal table that maps PCI ID to base baud[1] but now you are tied 
to the PCI subsystem and you get into issues of no output until after PCI 
enumeration is done, what happens if you have 2 different PCI cards installed, 
what happens if you find a serial card that isn't on the list, what about 
Express cards, etc.  I thought it would be easier to just add a parameter to 
specify it similar to being able to specify the I/O port.  The hope is that 
most of the PCI serial cards out there do use the standard base baud so most 
people wouldn't have to worry about this parameter but it is available if 
necessary.

Having said all of that, I see that there is some PCI support in grub2 so I can 
look into creating such a table.  Even if we go that route I think we should 
still add the `--base' parameter, for those situations where the table doesn't 
work.

[1]  This is what the Linux driver does but this table is only available 
relatively late in the kernel boot process.  For early printk's I've submitted 
a patch to the LKML to allow you to specify the base baud on the kernel command 
line as a companion to this patch.

--
Don Dugger
"Censeo Toto nos in Kansa esse decisse." - D. Gale
address@hidden
Ph: (303)443-3786 

>-----Original Message-----
>From: address@hidden 
>[mailto:address@hidden 
>On Behalf Of Robert Millan
>Sent: Tuesday, November 04, 2008 8:40 AM
>To: The development of GRUB 2
>Subject: Re: [PATCH] PCI serial card support
>
>On Mon, Nov 03, 2008 at 04:38:02PM -0800, 
>address@hidden wrote:
>> The problem with using a PCI serial card for the console is 
>that many 
>> PCI cards use a different crystal than the IBM PC standard.  This 
>> means that serial drivers wind up computing the wrong divisor when 
>> trying to set the baud rate.  This patch solves this problem 
>by adding the `--base'
>> parameter to the `serial' command.  The allows you to set the base 
>> baud (typically the highest baud rate supported by the 
>device) so that 
>> PCI cards with non-standard crystal frequencies can be 
>supported.  For 
>> example, the option I use with my PCI serial card is:
>> 
>>      serial --port=0xe880 --speed=115200 --base=921600
>
>Hi!
>
>Is there no better way to do this than queriing the user?  Can 
>you read this info from the device itself, or from its PCI id?
>
>--
>Robert Millan
>
>  The DRM opt-in fallacy: "Your data belongs to us. We will 
>decide when (and
>  how) you may access your data; but nobody's threatening your 
>freedom: we
>  still allow you to remove your data and not access it at all."
>
>
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