scsi: ufs: core: Read device property for ref clock

UFS storage devices require bRefClkFreq attribute to be set to operate
correctly at high speed mode. The necessary value is determined by what the
SoC / board supports. The standard doesn't specify a method to query the
value, so the information needs to be fed in separately.

DT information feeds into setting up the clock framework, so platforms
using DT can get the UFS reference clock frequency from the clock
framework. A special node "ref_clk" from the clock array for the UFS
controller node is used as the source for the information.

On the platforms that do not use DT (e.g. Intel), the alternative mechanism
to feed the intended reference clock frequency is necessary. Specifying the
necessary information in DSD of the UFS controller ACPI node is an
alternative mechanism proposed in this patch. Those can be accessed via
firmware property facility in the kernel and in many ways simillar to
querying properties defined in DT.

This patch introduces a small helper function to query a predetermined ACPI
supplied property of the UFS controller, and uses it to attempt retrieving
reference clock value, unless that was already done by the clock
infrastructure.

Link: https://lore.kernel.org/r/20220715210230.1.I365d113d275117dee8fd055ce4fc7e6aebd0bce9@changeid
Reviewed-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Daniil Lunev <dlunev@chromium.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/Documentation/scsi/ufs.rst b/Documentation/scsi/ufs.rst
index fbac745b783c..885b1a736e3f 100644
--- a/Documentation/scsi/ufs.rst
+++ b/Documentation/scsi/ufs.rst
@@ -17,6 +17,8 @@ Universal Flash Storage
      3.2 UTP Transfer requests
      3.3 UFS error handling
      3.4 SCSI Error handling
+   4. BSG Support
+   5. UFS Reference Clock Frequency configuration
 
 
 1. Overview
@@ -193,3 +195,16 @@ UFS specifications can be found at:
 
 - UFS - http://www.jedec.org/sites/default/files/docs/JESD220.pdf
 - UFSHCI - http://www.jedec.org/sites/default/files/docs/JESD223.pdf
+
+5. UFS Reference Clock Frequency configuration
+==============================================
+
+Devicetree can define a clock named "ref_clk" under the UFS controller node
+to specify the intended reference clock frequency for the UFS storage
+parts. ACPI-based system can specify the frequency using ACPI
+Device-Specific Data property named "ref-clk-freq". In both ways the value
+is interpreted as frequency in Hz and must match one of the values given in
+the UFS specification. UFS subsystem will attempt to read the value when
+executing common controller initialization. If the value is available, UFS
+subsytem will ensure the bRefClkFreq attribute of the UFS storage device is
+set accordingly and will modify it if there is a mismatch.