linux-kernel - Re: [PATCH v3 04/15] phy: tegra: xusb: tegra210: Do not reset UPHY PLL

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Message-ID: <20200928130618.GE3065790@ulmo>
Date:   Mon, 28 Sep 2020 15:06:18 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     JC Kuo <jckuo@...dia.com>
Cc:     gregkh@...uxfoundation.org, robh@...nel.org, jonathanh@...dia.com,
        kishon@...com, linux-tegra@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, nkristam@...dia.com
Subject: Re: [PATCH v3 04/15] phy: tegra: xusb: tegra210: Do not reset UPHY
 PLL

On Wed, Sep 09, 2020 at 04:10:30PM +0800, JC Kuo wrote:
> Once UPHY PLL hardware power sequencer is enabled, do not assert
> reset to PEX/SATA PLLs, otherwise UPHY PLL operation will be broken.
> This commit removes reset_control_assert(pcie->rst) and
> reset_control_assert(sata->rst) from PEX/SATA UPHY disable procedure.
> 
> Signed-off-by: JC Kuo <jckuo@...dia.com>
> ---
> v3:
>    new, was a part of "phy: tegra: xusb: Rearrange UPHY init on Tegra210"
> 
>  drivers/phy/tegra/xusb-tegra210.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/phy/tegra/xusb-tegra210.c b/drivers/phy/tegra/xusb-tegra210.c
> index f06e7bc7a51b..ef4bbcbed60b 100644
> --- a/drivers/phy/tegra/xusb-tegra210.c
> +++ b/drivers/phy/tegra/xusb-tegra210.c
> @@ -504,7 +504,6 @@ static void tegra210_pex_uphy_disable(struct tegra_xusb_padctl *padctl)
>  	if (--pcie->enable > 0)
>  		goto unlock;
>  
> -	reset_control_assert(pcie->rst);
>  	clk_disable_unprepare(pcie->pll);
>  
>  unlock:
> @@ -746,7 +745,6 @@ static void tegra210_sata_uphy_disable(struct tegra_xusb_padctl *padctl)
>  	if (--sata->enable > 0)
>  		goto unlock;
>  
> -	reset_control_assert(sata->rst);
>  	clk_disable_unprepare(sata->pll);
>  
>  unlock:

Does this mean that we can no longer reset these PLLs anymore? Is that
safe? Would we ever need to reset them for recovery or similar? For
power saving, is disabling the clock enough, or could we save some extra
power by putting the PLLs into reset?

Thierry

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