Re: [PATCH v3 1/7] phy: Distinguish between Rx and Tx for MIPI D-PHY with submodes

On 06/08/21 01:11PM, Paul Kocialkowski wrote:

Hi,

On Fri 25 Jun 21, 00:11, Pratyush Yadav wrote:

quoted

From: Paul Kocialkowski <redacted>

As some D-PHY controllers support both Rx and Tx mode, we need a way for
users to explicitly request one or the other. For instance, Rx mode can
be used along with MIPI CSI-2 while Tx mode can be used with MIPI DSI.

Introduce new MIPI D-PHY PHY submodes to use with PHY_MODE_MIPI_DPHY.
The default (zero value) is kept to Tx so only the rkisp1 driver, which
uses D-PHY in Rx mode, needs to be adapted.

After some thinking and discussions, it appears that using the submode is
probably not the best way to distinguish between rx and tx. This is because
rx/tx is more of a specification of the hardware component than a run-time
descision. Indeed the D-PHY blocks are usually dedicated to an associated
controller (DSI or CSI-2) and thus each instance is either meant for tx or
rx use.

Ok. IIRC Laurent also brought this point up earlier as well. At that 
time I took the allwinner DPHY as an example of a DPHY that can run in 
both modes.

The Cadence DPHY also supports both Rx and Tx modes but I don't know if 
both can be implemented at the same time, if that would even make any 
sense.

As a result I will be using the allwinner,direction string property in
device-tree instead of the submode, with values of either "rx" or "tx".
I suppose you can do something similar if you agree it makes more sense.

Wouldn't a different compatible a better idea?

Cheers,

Paul
 

quoted

Signed-off-by: Paul Kocialkowski <redacted>
Signed-off-by: Pratyush Yadav <redacted>
---

(no changes since v1)

 include/linux/phy/phy-mipi-dphy.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/include/linux/phy/phy-mipi-dphy.h b/include/linux/phy/phy-mipi-dphy.h
index a877ffee845d..0f57ef46a8b5 100644
--- a/include/linux/phy/phy-mipi-dphy.h
+++ b/include/linux/phy/phy-mipi-dphy.h

@@ -6,6 +6,19 @@
 #ifndef __PHY_MIPI_DPHY_H_
 #define __PHY_MIPI_DPHY_H_
 
+/**
+ * enum phy_mipi_dphy_submode - MIPI D-PHY sub-mode
+ *
+ * A MIPI D-PHY can be used to transmit or receive data.
+ * Since some controllers can support both, the direction to enable is specified
+ * with the PHY sub-mode. Transmit is assumed by default with phy_set_mode.
+ */
+
+enum phy_mipi_dphy_submode {
+	PHY_MIPI_DPHY_SUBMODE_TX = 0,
+	PHY_MIPI_DPHY_SUBMODE_RX,
+};
+
 /**
  * struct phy_configure_opts_mipi_dphy - MIPI D-PHY configuration set
  *

-- 
2.30.0

-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.

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