Re: [LinuxBIOS] PCI device memory resource

[Myles Watson]

I think the confusion comes because of the difference between memory and
memory address space.  The PCI controller is asking for 32 MB of the
physical address space, not memory.  When the BIOS allocates this region in
the address space, it is trusting that the PCI controller will respond to
any reads/writes to that address space.

There is no need to have actual RAM backing up every bit of address space,
but the device needs to respond to accesses to its address space.

Myles

_____

From: Baski [mailto:[e-mail]] 
Sent: Thursday, January 10, 2008 8:14 AM
To: [e-mail]; [e-mail]
Subject: RE: [LinuxBIOS] PCI device memory resource

Pardon my bad phrasing of the original question.  I have a mem-mapped PCI
controller which has no on-board memory, but is asking for 32MB memory
resource.  Is this legal?  While BIOS gives it 32MB address space, who is
going to malloc and give it the required memory to work with?
Thanks - Baski
Myles Watson  wrote:

I'm guessing that you're asking if it has to have as much memory as the
resource.  If that's the case, the answer is no.  You just have to respond
to any request in that region.

In other words, you could request a 1 GB region and only respond with useful
data in the first 1 MB (respond to any other read with zeros), or map the 1
MB 1024 times into the 1 GB, or anything else you decide.

Sorry if I totally missed the intent of your question,

Myles

_____

From: [e-mail]
[mailto:[e-mail]] On Behalf Of Baski
Sent: Wednesday, January 09, 2008 7:06 PM
To: [e-mail]
Subject: [LinuxBIOS] PCI device memory resource

For a PCI device to request memory resource of ,say 1MB, should it have
onboard
memory of 1MB ?
TIA

_____

Never miss a thing. Make Yahoo
http://us.rd.yahoo.com/evt=51438/*http:/www.yahoo.com/r/hs  your homepage.

_____

Never miss a thing. Make Yahoo
http://us.rd.yahoo.com/evt=51438/*http:/www.yahoo.com/r/hs  your homepage.