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From:   Rasmus Villemoes <linux@rasmusvillemoes.dk>
To:     netdev@vger.kernel.org, Andrew Lunn <andrew@lunn.ch>,
        Heiner Kallweit <hkallweit1@gmail.com>,
        Russell King <linux@armlinux.org.uk>
Cc:     devicetree@vger.kernel.org, Rob Herring <robh+dt@kernel.org>,
        Jakub Kicinski <kuba@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Grygorii Strashko <grygorii.strashko@ti.com>,
        Praneeth Bajjuri <praneeth@ti.com>,
        linux-kernel@vger.kernel.org,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Rob Herring <robh@kernel.org>
Subject: [PATCH net-next v2 1/3] dt-bindings: dp83867: add binding for io_impedance_ctrl nvmem cell
Date:   Tue, 14 Jun 2022 10:46:10 +0200
Message-Id: <20220614084612.325229-2-linux@rasmusvillemoes.dk>
In-Reply-To: <20220614084612.325229-1-linux@rasmusvillemoes.dk>
References: <20220606202220.1670714-1-linux@rasmusvillemoes.dk>
 <20220614084612.325229-1-linux@rasmusvillemoes.dk>
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We have a board where measurements indicate that the current three
options - leaving IO_IMPEDANCE_CTRL at the reset value (which is
factory calibrated to a value corresponding to approximately 50 ohms)
or using one of the two boolean properties to set it to the min/max
value - are too coarse.

There is no fixed mapping from register values to values in the range
35-70 ohms; it varies from chip to chip, and even that target range is
approximate. So add a DT binding for an nvmem cell which can be
populated during production with a value suitable for each specific
board.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
 .../devicetree/bindings/net/ti,dp83867.yaml    | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/Documentation/devicetree/bindings/net/ti,dp83867.yaml b/Documentation/devicetree/bindings/net/ti,dp83867.yaml
index 047d757e8d82..76ff08a477ba 100644
--- a/Documentation/devicetree/bindings/net/ti,dp83867.yaml
+++ b/Documentation/devicetree/bindings/net/ti,dp83867.yaml
@@ -31,6 +31,16 @@ properties:
   reg:
     maxItems: 1
 
+  nvmem-cells:
+    maxItems: 1
+    description:
+      Nvmem data cell containing the value to write to the
+      IO_IMPEDANCE_CTRL field of the IO_MUX_CFG register.
+
+  nvmem-cell-names:
+    items:
+      - const: io_impedance_ctrl
+
   ti,min-output-impedance:
     type: boolean
     description: |
@@ -42,9 +52,11 @@ properties:
     description: |
       MAC Interface Impedance control to set the programmable output impedance
       to a maximum value (70 ohms).
-      Note: ti,min-output-impedance and ti,max-output-impedance are mutually
-        exclusive. When both properties are present ti,max-output-impedance
-        takes precedence.
+      Note: Specifying an io_impedance_ctrl nvmem cell or one of the
+        ti,min-output-impedance, ti,max-output-impedance properties
+        are mutually exclusive. If more than one is present, an nvmem
+        cell takes precedence over ti,max-output-impedance, which in
+        turn takes precedence over ti,min-output-impedance.
 
   tx-fifo-depth:
     $ref: /schemas/types.yaml#/definitions/uint32
-- 
2.31.1