Thanks Keith.
Let's take a x86 world as of now, and let's say the physical address
(returned by virt_to_phys()) is 0661a070.
The pci address (as stated) is e2c20000.
Since the BAR0-region is of size 256 bytes, so the system-agent (as
per x86-terminology) will monitor the highest 24 bits of
address-lines, to sense a MMIO read/write, and then forward the
transaction to the corresponding pci bridge/device.
So, in the present case, would
a)
The system-agent sense address-lines A31-A8 value as 0661a07? If yes,
is it the system-agent that does the translation from 0661a070 =>
e2c20000, before finally forwarding the transaction to pci
bridge/device?
b)
The system-agent sense address-lines A31-A8 value as e2c2000 (and
simply forwards the transaction to pci bridge/device)? If yes,
who/what does the translation from 0661a070 =? e2c20000?
Meanwhile, I am also trying to learn how to do kernel-development for
statically linked modules (like pci).
That would help in a much better understanding of the things-flow :P
Thanks for the help.
Thanks and Regards,
Ajay
On Fri, Oct 1, 2021 at 8:43 PM Keith Busch <kbusch@xxxxxxxxxx> wrote:
>
> On Fri, Oct 01, 2021 at 08:21:06PM +0530, Ajay Garg wrote:
> > Hi All.
> >
> > I have a SD/MMC reader over PCI, which displays the following (amongst
> > others) when we do "lspci -vv" :
> >
> > #########################################################
> > Region 0: Memory at e2c20000 (32-bit, non-prefetchable) [size=512]
> > #########################################################
> >
> > Above shows that e2c20000 is the physical (base-)address of BAR0.
> >
> > Now, in the device driver, I do the following :
> >
> > ########################################################
> > .....
> > struct pci_dev *ptr;
> > void __iomem *bar0_ptr;
> > ......
> >
> > ......
> > pci_request_region(ptr, 0, "ajay_sd_mmc_BAR0_region");
> > bar0_ptr = pci_iomap(ptr, 0, pci_resource_len(ptr, 0));
> >
> > printk("Base virtual-address = [%p]\n", bar0_ptr);
> > printk("Base physical-address = [%p]\n", virt_to_phys(bar0_ptr));
> > printk("Base bus-address = [%p]\n", virt_to_bus(bar0_ptr));
> >
> > I have removed error-checking, but I confirm that pci_request_region()
> > and pci_iomap calls are successful.
> >
> > Now, in the 3 printk's, none of the value is printed as e2c20000.
> > I was expecting that the 2nd result, of virt_to_phys() translation,
> > would be equal to the base-address of BAR0 register, as reported by
> > lspci.
> >
> >
> > What am I missing?
> > Will be grateful for pointers.
>
> The CPU address isn't always the same as the PCI address. For example,
> some memory resources are added via pci_add_resource_offset(), so the
> windows the host sees will be different than the ones the devices use.
