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

[Philipp Zabel]

On Di, 2022-03-22 at 03:22 +0000, Dylan Hung wrote:
> > -----Original Message-----
> > From: Andrew Lunn [mailto:andrew@xxxxxxx]
> > Sent: 2022年3月22日 11:01 AM
> > To: Dylan Hung <dylan_hung@xxxxxxxxxxxxxx>
> > Cc: Krzysztof Kozlowski <krzk@xxxxxxxxxx>; robh+dt@xxxxxxxxxx;
> > joel@xxxxxxxxx; andrew@xxxxxxxx; hkallweit1@xxxxxxxxx;
> > linux@xxxxxxxxxxxxxxx; davem@xxxxxxxxxxxxx; kuba@xxxxxxxxxx;
> > pabeni@xxxxxxxxxx; p.zabel@xxxxxxxxxxxxxx; 
> > devicetree@xxxxxxxxxxxxxxx;
> > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> > linux-aspeed@xxxxxxxxxxxxxxxx;
> > linux-kernel@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; BMC-SW
> > <BMC-SW@xxxxxxxxxxxxxx>; stable@xxxxxxxxxxxxxxx
> > 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@xxxxxxxxxx]
> > > > Sent: 2022年3月21日 11:53 PM
> > > > To: Dylan Hung <dylan_hung@xxxxxxxxxxxxxx>; robh+dt@xxxxxxxxxx;
> > > > joel@xxxxxxxxx; andrew@xxxxxxxx; andrew@xxxxxxx;
> > > > hkallweit1@xxxxxxxxx; linux@xxxxxxxxxxxxxxx; 
> > > > davem@xxxxxxxxxxxxx;
> > > > kuba@xxxxxxxxxx; pabeni@xxxxxxxxxx; p.zabel@xxxxxxxxxxxxxx;
> > > > devicetree@xxxxxxxxxxxxxxx; 
> > > > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> > > > linux-aspeed@xxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > > > netdev@xxxxxxxxxxxxxxx
> > > > Cc: BMC-SW <BMC-SW@xxxxxxxxxxxxxx>; stable@xxxxxxxxxxxxxxx
> > > > 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@xxxxxxxxxxxxxx>
> > > > > Cc: stable@xxxxxxxxxxxxxxx
> > > > 
> > > > 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