mlx5 4K UAR

The following series of patches optimizes the usage of the UAR area which is
contained within the BAR 0-1. Previous versions of the firmware and the driver
assumed each system page contains a single UAR. This patch set will query the
firmware for a new capability that if published, means that the firmware can
support UARs of fixed 4K regardless of system page size. In the case of
powerpc, where page size equals 64KB, this means we can utilize 16 UARs per
system page. Since user space processes by default consume eight UARs per
context this means that with this change a process will need a single system
page to fulfill that requirement and in fact make use of more UARs which is
better in terms of performance.

In addition to optimizing user-space processes, we introduce an allocator
that can be used by kernel consumers to allocate blue flame registers
(which are areas within a UAR that are used to write doorbells). This provides
further optimization on using the UAR area since the Ethernet driver makes
use of a single blue flame register per system page and now it will use two
blue flame registers per 4K.

The series also makes changes to naming conventions and now the terms used in
the driver code match the terms used in the PRM (programmers reference manual).
Thus, what used to be called UUAR (micro UAR) is now called BFREG (blue flame

In order to support compatibility between different versions of
library/driver/firmware, the library has now means to notify the kernel driver
that it supports the new scheme and the kernel can notify the library if it
supports this extension. So mixed versions of libraries can run concurrently
without any issues.

        Eli and Matan
Version: GnuPG v1

net/mlx5: Activate support for 4K UARs

Activate 4K UAR support for firmware versions that support it.

Signed-off-by: Eli Cohen <>
Reviewed-by: Matan Barak <>
Signed-off-by: Leon Romanovsky <>
Signed-off-by: Saeed Mahameed <>
1 file changed