Re: pci-mvebu driver on km_kirkwood

[Gerlando Falauto <gerlando.falauto@keymile.com>]

Dear Thomas,

On 02/21/2014 02:47 PM, Thomas Petazzoni wrote:
> Dear Gerlando Falauto,
>
> On Fri, 21 Feb 2014 13:24:36 +0100, Gerlando Falauto wrote:
>
>> So I restored the total aperture size to 192MB.
>> I had to rework your patch a bit because:
>>
>> a) I'm running an older kernel and driver
>> b) sizes are actually 1-byte offset
>
> Hum, right. This is a bit weird, maybe I should change that, I don't
> think the mvebu-mbus driver should accept 1-byte offset sizes.

I don't know anything about this, I only know the size dumped is of the 
form 0x...ffff, that's all.

>> Here's the assignment (same as before):
>>
>> pci 0000:00:01.0: BAR 8: assigned [mem 0xe0000000-0xebffffff]
>> pci 0000:01:00.0: BAR 1: assigned [mem 0xe0000000-0xe7ffffff]
>> pci 0000:01:00.0: BAR 3: assigned [mem 0xe8000000-0xe87fffff]
>> pci 0000:01:00.0: BAR 4: assigned [mem 0xe8800000-0xe8801fff]
>> pci 0000:01:00.0: BAR 0: assigned [mem 0xe8802000-0xe8802fff]
>> pci 0000:01:00.0: BAR 2: assigned [mem 0xe8803000-0xe8803fff]
>> pci 0000:01:00.0: BAR 5: assigned [mem 0xe8804000-0xe8804fff]
>>
>> And here's the output I get from:
>>
>> # cat /sys/kernel/debug/mvebu-mbus/devices
>> [00] 00000000e8000000 - 00000000ec000000 : pcie0.0 (remap 00000000e8000000)
>> [01] disabled
>> [02] disabled
>> [03] disabled
>> [04] 00000000ff000000 - 00000000ff010000 : nand
>> [05] 00000000f4000000 - 00000000f8000000 : vpcie
>> [06] 00000000fe000000 - 00000000fe010000 : dragonite
>> [07] 00000000e0000000 - 00000000e8000000 : pcie0.0
>
> This seems correct: we have two windows pointing to the same device,
> and they have consecutive addresses.

I don't know how to interpret the (remap ... ) bit, but yes, this looks 
right to me as well. I just don't know why mbus window 7 gets picked 
before 0, but apart from that, it looks nice.

>> I did not get to test the whole address space thoroughly, but all the
>> BARs are still accessible (mainly BAR0 which contains the control space
>> and is mapped on the "new" MBUS window, and BAR1 which is the "big"
>> one). So at least, the issues we had before are now gone.
>
> Did you check that what you read from BAR0 (which is mapped on the new
> MBUS window) is really what you expect, and not just the same thing as
> BAR1 accessible for the big window? I just want to make sure that the
> hardware indeed properly handles two windows for the same device.

Yes, there's no way the two BARs could be aliased. It's a fairly complex 
FPGA design, where BAR1 is the huge address space for a PCI-to-localbus 
bridge (whose connected devices are recognized correctly) and BAR0 is 
the control BAR (and its registers are read and written without a problem).


>> So I'd say this looks like a very promising approach. :-)
>
> Indeed. However, I don't think this approach solves the entire problem,
> for two reasons:
>
>   *) For small BARs that are not power-of-two sized, we may not want to
>      consume two windows, but instead consume a little bit more address
>      space. Using two windows to map a 96 KB BAR would be a waste of
>      windows: using a single 128 KB window is much more efficient.
>
>   *) I don't know if the algorithm to split the BAR into multiple
>      windows is going to be trivial.

I see others have already replied and I pretty much agree with them.

Thanks,
Gerlando