Hi
This is in reference to my previous post on plug and play:
I still don't understand few things and would be very glad if any one can help me.
Lets look at the PCI example as stated in LDD book.
So,
when system starts up it is said in the book that BIOS reads the
configuration space and allocates the memory and I/O regions, writes
back to configuration space, which can be used by the driver to access
the device.
Now I don't understand, how firmware knows which devices are present and how to access their configuration space ?
Book
also says there is 4 bytes of configuration space which holds the
unique function ID in each device so that driver can identify its
device (geographical addressing) but later it says that there are three
registers (device ID, vendor ID and class) which driver can use to
identify the device. Isn't its contradictory? Where is this unique
function ID ? Can any one make the idea of geographical addressing
clear ?
Then it talks of id tables which drivers uses to tell what
devices it can handle, which I understand is for hot plugging because
then system has the list and if later by some means system able to
figure out that there is new device attached to it, it can refer to
this table to find the appropriate driver.
Then it talks of registering the driver.. which when I looked in to the code goes like this
pci_register_driver
-> device_register -> bus_add_driver -> driver_attach (match
this driver against every device on that bus) -> driver_probe_device
-> pci_device_probe -> ultimately calls driver probe.. and if
everything goes well driver will get configure to device.
So what I understood is, if you add new driver and if
(somehow, I dont understand how) system has list of devices attach to
that bus, we can match the driver and the device. Does it mean that
while system boots up it calls all functions with label "__init"
(implying every driver registers itself) ?
Then book talks about the kernel functions to access the configuration space.
Now, after reading this, I still dont understand how the system maintains the list of devices it has on a particular bus ?
Similar
to driver register function there is device register function which
takes device as an argument, which when I looked goes like this
device_register -> device_add -> bus_add_device -> device_attach
Now, what is the use of this and who calls this ? how is this linked to PCI ?
Can any one please please make the things clear ?
Thank you very much
Regards
--
Kamal Kant Gupta
