Re: Add a "enable" sysfs attribute to the pci devices to allow userspace (Xorg) to enable devices without doing foul direct access

[Kyle Moffett <mrmacman_g4@mac.com>]

On May 7, 2006, at 08:05:59, Krzysztof Halasa wrote:
> Kyle Moffett <mrmacman_g4@mac.com> writes:
>> Jon Smirl gave a great description of exactly how to write such a  
>> "driver".  I seem to recall that we already have the ability to  
>> trigger manual PCI binding by bus:slot number; in combination with  
>> an appropriate "write EEPROM with firmware file" driver that has  
>> no default list of PCI devices; you could easily manually trigger  
>> a bind of the device.
>
> Writing EEPROM is not a problem and can be done safely from user  
> space (mmap /dev/mem).

This is *exactly* what we don't want to do!  The whole point of this  
thread is to prevent the need to use /dev/mem and /dev/kmem for  
anything except debugging.

> Doing it in the kernel seems like an overkill, especially if you do  
> the operation once in few years it's much easier to just download a  
> (statically linked?) binary than messing with the kernel.

Ewww, I certainly wouldn't trust a binary statically-linked binary  
program that mmaps /dev/mem or /dev/kmem, and I certainly bet that  
90% of the people on this list would feel likewise.  We'd much prefer  
a program which does this:

   #! /bin/sh
   cp firmware.bin /lib/firmware/some_firmware_file.bin
   echo -n eeprom_load_driver >/sys/device/$PCI_ID/bind
   echo -n 1 >/sys/device/$PCI_ID/unbind

Simple, obviously correct, and uses a nice reuseable driver too!

> It doesn't even interfere with the "main" driver and can be done  
> while the device is operating (given that previous EEPROM made  
> sense, otherwise the driver would not load).

No!  That would be even worse!  You're then having userspace poke at  
the driver while a kernel driver is loaded, which is *exactly* what X  
is getting into trouble for doing.  If you want to add firmware  
update capability, add it to the preexisting primary driver.

>> In any case what you really need for all those cases is a  
>> simplistic stub driver that provides some sort of in-kernel mutual  
>> exclusion.
>
> Right. I.e., "enable" interface with, possibly, locking mechanism,  
> instead of some per-class "driver".

No, not an "enable" interface.  In this case the kernel should do  
basically all of the poking at PCI resources for you.  If you  
_really_ want to do that kind of update in userspace, write a stub  
driver which just enables the device on bind, disables it on unbind,  
and mmap and write to the sysfs "rom" file.

Cheers,
Kyle Moffett