linux-kernel - Re: [EXT] Re: [v2 01/11] irqchip: ls-extirq: Add LS1043A, LS1088A external interrupt

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Date:   Tue, 3 Nov 2020 09:02:36 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Leo Li <leoyang.li@....com>,
        "Biwen Li (OSS)" <biwen.li@....nxp.com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "Z.q. Hou" <zhiqiang.hou@....com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "jason@...edaemon.net" <jason@...edaemon.net>,
        "maz@...nel.org" <maz@...nel.org>
Cc:     "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jiafei Pan <jiafei.pan@....com>,
        Xiaobo Xie <xiaobo.xie@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [EXT] Re: [v2 01/11] irqchip: ls-extirq: Add LS1043A, LS1088A
 external interrupt

On 02/11/2020 22.22, Leo Li wrote:
>>>
>>> Where did you get this information that the register on LS1043 and
>>> LS1046 is bit reversed?  I cannot find such information in the RM.
>>> And does this mean all other SCFG registers are also bit reversed?  If
>>> this is some information that is not covered by the RM, we probably
>>> should clarify it in the code and the commit message.
>> Hi Leo,
>>
>> I directly use the same logic to write the bit(field IRQ0~11INTP) of the
>> register SCFG_INTPCR in LS1043A and LS1046A.
>> Such as,
>> if I want to control the polarity of IRQ0(field IRQ0INTP, IRQ0 is active low) of
>> LS1043A/LS1046A, then I just need write a value 1 << (31 - 0) to it.
>> The logic depends on register's definition in LS1043A/LS1046A's RM.
> 
> Ok.  The SCFG_SCFGREVCR seems to be a one-off fixup only existed on LS1021.  And it is mandatory to be bit_reversed according to the RM which is already taken care of in the RCW.  So the bit reversed case should be the only case supported otherwise a lot of other places for SCFG access should be failed.
> 
> I think we should remove the bit_reverse thing all together from the driver for good.  This will prevent future confusion.  Rasmus, what do you think?

Yes, all the ls1021a-derived boards I know of do have something like

# Initialize bit reverse of SCFG registers
09570200 ffffffff

in their pre-boot-loader config file. And yes, the RM does say

  This register must be written 0xFFFF_FFFF as a part of
  initialization sequence before writing to any other SCFG
  register.

but nowhere does it say "or else...", nor a little honest addendum
"because we accidentally released broken silicon with this misfeature
_and_ wrong POR value".

Can we have an official statement from NXP stating that SCFGREVCR is a
hardware design bug? And can you send it through a time-machine so I had
it three years ago avoiding the whole "fsl,bit-reverse
device-tree-property, no, read the register if you're on a ls1021a and
decide" hullabaloo.

Rasmus