[U-Boot] [PATCH 1/8] pci: Make PCI bridge memory alignment configurable

[Daniel Schwierzeck]

On 21.11.2017 21:33, Paul Burton wrote:
> On some systems aligning PCI memory to a 1MB boundary every time a
> bridge is encountered may lead to exhausting the available memory space
> before all devices have been assigned addresses.
> 
> For example on the MIPS Boston development board we have an Intel EG20T
> Platform Controller Hub connected to a Xilinx AXI to PCIe root port
> which is only assigned a 1MB memory region. The Intel EG20T contains a
> bridge device beneath which all of its peripheral devices can be found,
> and that bridge device contains a ROM. If we align to 1MB when we
> encounter each bridge device we therefore do something like this:
> 
>   - Start with bus_lower at 0x16000000.
> 
>   - Find the Xilinx root bridge, which has no visible BARs so we do very
>     little to it.
> 
>   - Probe the bus beneath the Xilinx bridge device, aligning bus_lower
>     to a 1MB boundary first. That leaves it still at 0x16000000.
> 
>   - Find the EG20T bridge device, which we find has a 64KiB ROM. We
>     assign it the address range 0x16000000-0x1600ffff which leaves
>     bus_lower at 0x16010000.
> 
>   - Probe the bus beneath the EG20T bridge device, aligning bus_lower to
>     a 1MB boundary first. This leaves bus_lower at 0x16100000, which is
>     the end of the available memory space.
> 
>   - Find the various peripheral devices the EG20T contains, but fail to
>     assign any memory space to them since bus_lower is at the end of the
>     memory space available to the PCI bus.
> 
> This patch allows that 1MB alignment to be changed or disabled via
> Kconfig, so that systems such as this can select an alignment which
> works for them.
> 
> Signed-off-by: Paul Burton <paul.burton at imgtec.com>
> Cc: Daniel Schwierzeck <daniel.schwierzeck at gmail.com>
> Cc: Simon Glass <sjg at chromium.org>
> Cc: u-boot at lists.denx.de
> Signed-off-by: Paul Burton <paul.burton at mips.com>
> ---
> 
>  drivers/pci/Kconfig    |  7 +++++++
>  drivers/pci/pci_auto.c | 24 ++++++++++++++++--------
>  2 files changed, 23 insertions(+), 8 deletions(-)
> 

Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck at gmail.com>

-- 
- Daniel

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