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

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Message-ID: <711f2561ac3d84bcd5bbe26723869b47@manjaro.org>
Date: Fri, 23 Aug 2024 07:45:07 +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 2024-08-22 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.

> 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,