linux-kernel - Re: [PATCH v4 3/4] mmc: dw_mmc-rockchip: Skip all phases bigger than 270 degrees

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Message-ID: <38952ff6affa5929612aaabbae3ca996@manjaro.org>
Date: Mon, 26 Aug 2024 16:52:26 +0200
From: Dragan Simic <dsimic@...jaro.org>
To: Detlev Casanova <detlev.casanova@...labora.com>
Cc: linux-kernel@...r.kernel.org, Ulf Hansson <ulf.hansson@...aro.org>, Rob
 Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor
 Dooley <conor+dt@...nel.org>, Heiko Stuebner <heiko@...ech.de>, Jaehoon
 Chung <jh80.chung@...sung.com>, linux-mmc@...r.kernel.org,
 devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-rockchip@...ts.infradead.org, kernel@...labora.com, Shawn Lin
 <shawn.lin@...k-chips.com>
Subject: Re: [PATCH v4 3/4] mmc: dw_mmc-rockchip: Skip all phases bigger than
 270 degrees

Hello Detlev,

On 2024-08-23 15:59, Detlev Casanova wrote:
> On Friday, 23 August 2024 01:45:07 EDT Dragan Simic wrote:
>> Hello Detlev,
>> 
>> On 2024-08-22 23:15, Detlev Casanova wrote:
>> > From: Shawn Lin <shawn.lin@...k-chips.com>
>> >
>> > Per design recommendation, it'd better not try to use any phase
>> > which is bigger than 270. Let's officially follow this.
>> 
>> Would it be possible to provide a reference to the actual design
>> specification?  This change affects all users of the dw_mmc-rockchip
>> driver, so in case any regressions are found later, having as much
>> detail as possible can only be beneficial.
> 
> I don't have the reference and only trusting rockchip on this. This 
> could be
> specific to rockchip hardware.
> Anyway, the drivers works well on my side on my rk3576 armsom sige5 
> without
> this patch, so I'm willing to drop it completely.

I think it would be better if you'd drop it in this series, and submit
it later separately, as a follow-up patch, to reduce the chances for any
possible regressions.  Maybe we'll also have more background information
available by then, who knows.

>> > Signed-off-by: Shawn Lin <shawn.lin@...k-chips.com>
>> > (cherry picked from commit 2a53aab5cfa43065b2e979959d727332a8a03c03)
>> > Signed-off-by: Detlev Casanova <detlev.casanova@...labora.com>
>> > ---
>> >
>> >  drivers/mmc/host/dw_mmc-rockchip.c | 3 +++
>> >  1 file changed, 3 insertions(+)
>> >
>> > diff --git a/drivers/mmc/host/dw_mmc-rockchip.c
>> > b/drivers/mmc/host/dw_mmc-rockchip.c
>> > index 2748f9bf2691..1458cb5fd5c7 100644
>> > --- a/drivers/mmc/host/dw_mmc-rockchip.c
>> > +++ b/drivers/mmc/host/dw_mmc-rockchip.c
>> > @@ -310,6 +310,9 @@ static int dw_mci_rk3288_execute_tuning(struct
>> > dw_mci_slot *slot, u32 opcode)
>> >
>> >  	/* Try each phase and extract good ranges */
>> >  	for (i = 0; i < priv->num_phases; ) {
>> >
>> > +		/* Cannot guarantee any phases larger than 270 would
> work well */
>> > +		if (TUNING_ITERATION_TO_PHASE(i, priv->num_phases) >
> 270)
>> > +			break;
>> >
>> >  		rockchip_mmc_set_phase(host, true,
>> >
>> >  				       TUNING_ITERATION_TO_PHASE(
>> >
>> >  						i,