[linux-dvb] Re: [inbox] Re: Difference btw Binary Only Kernel Modules and Firmware

[Ralph Metzler <rjkm@metzlerbros.de>]

Egon Single writes:
 > > IMHO it's ok to have firmware in dedicated processors on extension
 > > hardware, as long as you have access to the necessary specifications for
 > > the communication protocol with other parts of the system (which is
 > > lacking for the av7110 firmware I admit)
 > 
 > This means that using the firmware approach does require additional
 > hardware. Still the firmware goes back to the DVB driver which then has
 > dirct access to kernel memory. So if things go wrong in the firmware,
 > effects can still show up in the kernel and a kernel developer has no chance
 > to analyze the cause of the error. Which is probably my words for what you

No, the firmware has no direct access to kernel memory. Any accesses
to kernel memory can be controlled and debugged by any kernel
developer by changing the source of the driver.

This will of course not be true for all hardware. Some might be able
to control DMA destinations from inside the firmware. But this is not
a problem specific to firmwares (no matter if they are already included in the
hardware, on-chip or in flash, or loaded by the driver).
Any hardware with DMA capabilities might do random accesses to main
memory. This can be caused by simple bugs in the hardware or even 
hardwired instructions to take over the machine (no, I have no example
of the latter). This problem could only be solved by also having GPLed
hardware. There are some GPLed hardware designs but don't hold your breath
waiting for all hardware vendors to release chip layouts ...

Regarding binary modules, everyone should read the recent discussion on
the LKML. One could say that the consensus is that anything directly derived 
from the Linux kernel has to be GPLed but the interpretation of what
is derived and what not (or constitutes fair use) differs extremely. 
Especially if there are ABI boundaries, where those are or if there is
an ABI for binary kernel modules at all (not according to Linus), 
etc. is very unclear.


Ralph



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