linux-kernel - Re: [PATCH v2 3/3] ARM: dts: aspeed: add reset properties into MDIO nodes

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Date:   Tue, 22 Mar 2022 10:08:07 +0100
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Dylan Hung <dylan_hung@...eedtech.com>,
        Andrew Lunn <andrew@...n.ch>
Cc:     Krzysztof Kozlowski <krzk@...nel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "joel@....id.au" <joel@....id.au>,
        "andrew@...id.au" <andrew@...id.au>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        BMC-SW <BMC-SW@...eedtech.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH v2 3/3] ARM: dts: aspeed: add reset properties into MDIO
 nodes

On Di, 2022-03-22 at 03:22 +0000, Dylan Hung wrote:
> > -----Original Message-----
> > From: Andrew Lunn [mailto:andrew@...n.ch]
> > Sent: 2022年3月22日 11:01 AM
> > To: Dylan Hung <dylan_hung@...eedtech.com>
> > Cc: Krzysztof Kozlowski <krzk@...nel.org>; robh+dt@...nel.org;
> > joel@....id.au; andrew@...id.au; hkallweit1@...il.com;
> > linux@...linux.org.uk; davem@...emloft.net; kuba@...nel.org;
> > pabeni@...hat.com; p.zabel@...gutronix.de; 
> > devicetree@...r.kernel.org;
> > linux-arm-kernel@...ts.infradead.org;
> > linux-aspeed@...ts.ozlabs.org;
> > linux-kernel@...r.kernel.org; netdev@...r.kernel.org; BMC-SW
> > <BMC-SW@...eedtech.com>; stable@...r.kernel.org
> > Subject: Re: [PATCH v2 3/3] ARM: dts: aspeed: add reset properties
> > into MDIO
> > nodes
> > 
> > On Tue, Mar 22, 2022 at 02:32:13AM +0000, Dylan Hung wrote:
> > > > -----Original Message-----
> > > > From: Krzysztof Kozlowski [mailto:krzk@...nel.org]
> > > > Sent: 2022年3月21日 11:53 PM
> > > > To: Dylan Hung <dylan_hung@...eedtech.com>; robh+dt@...nel.org;
> > > > joel@....id.au; andrew@...id.au; andrew@...n.ch;
> > > > hkallweit1@...il.com; linux@...linux.org.uk; 
> > > > davem@...emloft.net;
> > > > kuba@...nel.org; pabeni@...hat.com; p.zabel@...gutronix.de;
> > > > devicetree@...r.kernel.org; 
> > > > linux-arm-kernel@...ts.infradead.org;
> > > > linux-aspeed@...ts.ozlabs.org; linux-kernel@...r.kernel.org;
> > > > netdev@...r.kernel.org
> > > > Cc: BMC-SW <BMC-SW@...eedtech.com>; stable@...r.kernel.org
> > > > Subject: Re: [PATCH v2 3/3] ARM: dts: aspeed: add reset
> > > > properties
> > > > into MDIO nodes
> > > > 
> > > > On 21/03/2022 10:56, Dylan Hung wrote:
> > > > > Add reset control properties into MDIO nodes.  The 4 MDIO
> > > > > controllers in
> > > > > AST2600 SOC share one reset control bit SCU50[3].
> > > > > 
> > > > > Signed-off-by: Dylan Hung <dylan_hung@...eedtech.com>
> > > > > Cc: stable@...r.kernel.org
> > > > 
> > > > Please describe the bug being fixed. See stable-kernel-rules.
> > > 
> > > Thank you for your comment.
> > > The reset deassertion of the MDIO device was usually done by the
> > bootloader (u-boot).
> > > However, one of our clients uses proprietary bootloader and
> > > doesn't
> > > deassert the MDIO reset so failed to access the HW in kernel
> > > driver.
> > 
> > So are you saying mainline u-boot releases the reset?
> > 
> Yes, if the mdio devices are used in u-boot.
> 
> > > The reset deassertion is missing in the kernel driver since it
> > > was
> > > created, should I add a BugFix for the first commit of this
> > > driver?
> > 
> > Yes, that is normal. Ideally the kernel should not depend on u-
> > boot, because
> > often people want to use other bootloaders, e.g. barebox. You
> > should also
> > consider kexec, where one kernel hands over to another kernel,
> > without the
> > bootloader being involved. In such a situation, you ideally want to
> > assert and
> > deassert the reset just to clean away any state the old kernel left
> > around.
> > 
> > But please do note, that the reset is optional, since you need to
> > be able to
> > work with old DT blobs which don't have the reset property in them.
> > 
> 
> Thank you. I will let the reset property be optional and modify the
> error-checking in the driver accordingly in V3.

No need to change the error checking, just use 
devm_reset_control_get_optional_shared().


regards
Philipp