On Tue, 2019-12-03 at 10:31 -0600, Jeremy Linton wrote:

Hi,

On 11/26/19 3:19 AM, Nicolas Saenz Julienne wrote:

quoted

From: Jim Quinlan <redacted>

This adds a basic driver for Broadcom's STB PCIe controller, for now
aimed at Raspberry Pi 4's SoC, bcm2711.

Signed-off-by: Jim Quinlan <redacted>
Co-developed-by: Nicolas Saenz Julienne <redacted>
Signed-off-by: Nicolas Saenz Julienne <redacted>

---

Changes since v2:
   - Correct rc_bar2_offset sign
   - Invert IRQ clear and masking in setup code
   - Use bitfield.h, redo all register ops while keeping the register
     names intact
   - Remove all SHIFT register definitions
   - Get rid of all _RB writes
   - Get rid of of_data
   - Don't iterate over inexisting dma-ranges
   - Add comment regarding dma-ranges validation
   - Small cosmetic cleanups
   - Fix license mismatch
   - Set driver Kconfig tristate
   - Didn't add any comment about the controller not being I/O coherent
     for now as I wait for Jeremy's reply

I guess its fine.. In answer to the original query. It seems that this 
PCIe bridge requires explicit cache operations for DMA from PCIe 
endpoints. This wasn't obvious to me at first reading because I was 
assuming the custom DMA ops were strictly to deal with the stated DMA 
limits.

Thanks, I now see what you meant.

So if you end up respinning, it still might be worthy mentioning 
somewhere that this is a non-coherent PCIe implementation. I still hold 
much of my original reservations about pieces of this driver. 
Particularly, how it might look if someone wanted to boot the RPi using 
ACPI on linux. But, I was shown a clever bit of AML recently, which 
solves those problems for the RPi and the attached XHCI.

I don't know much about ACPI, but ultimately if you're booting trough ACPI,
you're unlikely to use device-tree at all, right? And if you where and this
driver clashed with your ACPI implementation you'd simply have to disable it on
the device-tree.

So, given how much time I've looked at the root port configuration/etc 
sections of this driver and I've not found a serious bug:

Reviewed-by: Jeremy Linton <redacted>

Thanks!

Regards,
Nicolas