Hi Tomi,

Thanks for the review.
On 23/07/25 13:36, Tomi Valkeinen wrote:

Hi,

On 04/07/2025 15:59, Devarsh Thakkar wrote:

quoted

Do read-modify-write so that we re-use the characterized reset value as
specified in TRM [1] to program calibration wait time which defines number
of cycles to wait for after startup state machine is in bandgap enable
state.

This fixes PLL lock timeout error faced while using RPi DSI Panel on TI's
AM62L and J721E SoC since earlier calibration wait time was getting
overwritten to zero value thus failing the PLL to lockup and causing
timeout.

[1] AM62P TRM (Section 14.8.6.3.2.1.1 DPHY_TX_DPHYTX_CMN0_CMN_DIG_TBIT2):
Link: https://www.ti.com/lit/pdf/spruj83

Cc: stable@vger.kernel.org
Fixes: 7a343c8bf4b5 ("phy: Add Cadence D-PHY support")
Signed-off-by: Devarsh Thakkar <devarsht@ti.com>
---
V4: No change
V3:
- Do read-modify-write to preserve reset value for calibration wait
   time
V2:
Introduced this as as separate patch

  drivers/phy/cadence/cdns-dphy.c | 4 +++-
  1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/phy/cadence/cdns-dphy.c b/drivers/phy/cadence/cdns-dphy.c
index da8de0a9d086..24a25606996c 100644
--- a/drivers/phy/cadence/cdns-dphy.c
+++ b/drivers/phy/cadence/cdns-dphy.c

@@ -30,6 +30,7 @@
  
  #define DPHY_CMN_SSM			DPHY_PMA_CMN(0x20)
  #define DPHY_CMN_SSM_EN			BIT(0)
+#define DPHY_CMN_SSM_CAL_WAIT_TIME	GENMASK(8, 1)
  #define DPHY_CMN_TX_MODE_EN		BIT(9)
  
  #define DPHY_CMN_PWM			DPHY_PMA_CMN(0x40)

@@ -410,7 +411,8 @@ static int cdns_dphy_power_on(struct phy *phy)
  	writel(reg, dphy->regs + DPHY_BAND_CFG);
  
  	/* Start TX state machine. */
-	writel(DPHY_CMN_SSM_EN | DPHY_CMN_TX_MODE_EN,
+	reg = readl(dphy->regs + DPHY_CMN_SSM);
+	writel((reg & DPHY_CMN_SSM_CAL_WAIT_TIME) | DPHY_CMN_SSM_EN | DPHY_CMN_TX_MODE_EN,
  	       dphy->regs + DPHY_CMN_SSM);

That's not how you do read-modify-write. You should first read the
register, then clear the fields you want to set/clear, then set the
fields, then write.

reg = readl(dphy->regs + DPHY_CMN_SSM, dphy->regs + DPHY_CMN_SSM);
reg &= ~(DPHY_CMN_SSM_EN | DPHY_CMN_TX_MODE_EN)
reg |= DPHY_CMN_SSM_EN | DPHY_CMN_TX_MODE_EN;
writel(reg, dphy->regs + DPHY_CMN_SSM);

That's the general form, in this particular case the and-line is not
necessary, of course.

There's also FIELD_MODIFY() (and related), but I'm not sure if I like
them... Up to you.

As discussed offline, here we just wanted to preserve the value for 
DPHY_CMN_SSM_CAL_WAIT_TIME bits as these are holding the calibration 
wait time, reset rest and then enable the SSM by setting DPHY_CMN_SSM_EN 
| DPHY_CMN_TX_MODE_EN and the patch rightly achieves this. I assume we 
are aligned on this as I see your review here [1].

Kindly let me know if otherwise.

[1]: 
https://lore.kernel.org/all/2bec3583-6078-4650-a8d0-6cfe8fcec3f3@ideasonboard.com/ (local)

Regards
Devarsh

  Tomi

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