linux-kernel - Re: [PATCH] phy: cadence: cdns-dphy: Fix PLL lock and common ready poll timeout

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Message-ID: <c49f1741-d03a-08f2-ddb1-3b0462a67790@ti.com>
Date: Mon, 3 Feb 2025 13:29:59 +0530
From: Devarsh Thakkar <devarsht@...com>
To: Jai Luthra <jai.luthra@...asonboard.com>
CC: <vkoul@...nel.org>, <kishon@...nel.org>, <mripard@...nel.org>,
        <linux-phy@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <sakari.ailus@...ux.intel.com>, <vigneshr@...com>,
        <aradhya.bhatia@...ux.dev>, <s-jain1@...com>, <r-donadkar@...com>,
        <tomi.valkeinen@...asonboard.com>, <j-choudhary@...com>,
        <h-shenoy@...com>, <praneeth@...com>, <u-kumar1@...com>
Subject: Re: [PATCH] phy: cadence: cdns-dphy: Fix PLL lock and common ready
 poll timeout

Hi Jai,

On 30/12/24 19:12, Jai Luthra wrote:
> Hi Devarsh,
> 
> Thanks for the patch, must have been a fun debug :)
> 

Thanks for the review. Oh yeah indeed :).

<snip>
>> 1) PLL lockup and O_CMN_READY assertion can only happen after common state
>>    machine gets enabled, but driver was polling them before the common
>>    state machine was enabled. To fix this, add new function callbacks for
>>    polling on PLL lock and O_CMN_READY assertion and call them only after
>>    common state machine gets enabled.
>>
>> 2) The cadence DPHY IP registers (as described in J721E TRM [2]) has
>>    default reset values for register fields in some of the registers
>>    which were getting reset to 0 as driver was not preserving them and
>>    overwriting those bits to 0 while updating the registers thus impacting
>>    the overall PLL lockup time. For e.g. DPHY_TX_CMN0_CMN_DIG_TBIT2 has
>>    bits 1-8 used for PLL wait time calibrations with default value as 0x14h
>>    and DPHY_TX_CMN0_CMN_DIG_TBIT10 has bits 27-20 used for PWM Byteclock
>>    divider which is default set to 0x8. To avoid resetting these register
>>    bit-fields, perform read-modify-write while updating above registers.
> 
> IMHO these are separate changes, and thus should be separate patches, 
> even if they are both done to reduce the time spent in the wait loop.
> 
> Ideally first patch to fix (2) across the driver, checking if there are 
> any other registers with default values that are being overwritten.
> 
> And the second patch to fix (1)

Yes that sounds like a good idea indeed. Will fix this in V2 and re-spin.

Regards
Devarsh