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-rw-r--r--Documentation/scsi/ufs.rst15
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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.