Message-ID: <0470221e-0561-0c6f-1caf-9cf2f1679aa5@meizu.com>
Date:   Thu, 7 Apr 2022 10:19:31 +0800
From:   baihaowen <baihaowen@...zu.com>
To:     Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vineeth Vijayan <vneethv@...ux.ibm.com>
CC:     Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        <linux-s390@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2] s390: Simplify the calculation of variables

在 4/7/22 12:44 AM, Peter Oberparleiter 写道:
> On 06.04.2022 10:45, Heiko Carstens wrote:
>> On Wed, Apr 06, 2022 at 10:37:31AM +0800, Haowen Bai wrote:
>>> Fix the following coccicheck warnings:
>>> ./arch/s390/include/asm/scsw.h:695:47-49: WARNING
>>>  !A || A && B is equivalent to !A || B
>>>
>>> I apply a readable version just to get rid of a warning.
>>>
>>> Signed-off-by: Haowen Bai <baihaowen@...zu.com>
>>> ---
>>> V1->V2: apply a readable and simple version as suggestion.
>>>
>>>  arch/s390/include/asm/scsw.h | 47 ++++++++++++++++++++++++++++++--------------
>>>  1 file changed, 32 insertions(+), 15 deletions(-)
>> [full quote below]
>>
>> Vineeth, Peter, could one of you please Review and or ACK the patch
>> below?
> This patch changes scsw->cmd access to scsw->tm access, which is
> incorrect, so I cannot ACK them as is.
>
> Also I'm somewhat torn on the general question if these functions should
> be changed:
>
> - the current implementation is unreadable => change it
> - the current implementation works => keep it
> - improvement patches like this one seem to appear regularly and consume
>   time in reviewing => change it
>
> If there was a new version that really improved readability, this would
> be really welcome. The problem is that the definition of readability is
> special for these functions: each of these functions implement a
> validity check based on text from the s390 Principles of Operations
> (PoP) document [1]. "Readable" for myself would mean: I can easily
> correlate the code to the text from the PoP so that I can spot errors or
> adjust code to changed text.
>
> I'm adding some examples how that could look like below. My question to
> the original author would be, if this is something they could implement,
> or if we'd rather do that at some point in time in the future by ourselves.
>
>>> diff --git a/arch/s390/include/asm/scsw.h b/arch/s390/include/asm/scsw.h
>>> index a7c3ccf681da..b7e65f96de3c 100644
>>> --- a/arch/s390/include/asm/scsw.h
>>> +++ b/arch/s390/include/asm/scsw.h
>>> @@ -508,9 +508,13 @@ static inline int scsw_cmd_is_valid_zcc(union scsw *scsw)
>>>   */
>>>  static inline int scsw_cmd_is_valid_ectl(union scsw *scsw)
>>>  {
>>> -	return (scsw->cmd.stctl & SCSW_STCTL_STATUS_PEND) &&
>>> -	       !(scsw->cmd.stctl & SCSW_STCTL_INTER_STATUS) &&
>>> -	       (scsw->cmd.stctl & SCSW_STCTL_ALERT_STATUS);
>>> +	if (!(scsw->tm.stctl & SCSW_STCTL_STATUS_PEND))
>>> +		return 0;
>>> +	if (scsw->tm.stctl & SCSW_STCTL_INTER_STATUS)
>>> +		return 0;
>>> +	if (scsw->tm.stctl & SCSW_STCTL_ALERT_STATUS)
>>> +		return 1;
>>> +	return 0;
>>>  }
> Here's the PoP text that is the base for this function (note ECTL=E):
>
> "The E bit is meaningful whenever the subchannel is status pending with
> alert status either alone or together with primary status, secondary
> status, or both."
>
> A readable version for me would therefore contain code that can easily
> be matched against that text, e.g. something like:
>
> /* Must be status pending. */
> if (!(scsw->cmd.stctl & SCSW_STCTL_STATUS_PEND))
>   return 0;
>
> /* Must have alert status. */
> if (!(scsw->cmd.stctl & SCSW_STCTL_ALERT_STATUS))
>   return 0;
>
> /* Must be alone or together with primary, secondary or both,
>  * => no intermediate status. */
> if (scsw->cmd.stctl & SCSW_STCTL_INTER_STATUS)
>   return 0;
>
> return 1;
>
>>>  /**
>>> @@ -522,10 +526,15 @@ static inline int scsw_cmd_is_valid_ectl(union scsw *scsw)
>>>   */
>>>  static inline int scsw_cmd_is_valid_pno(union scsw *scsw)
>>>  {
>>> -	return (scsw->cmd.fctl != 0) &&
>>> -	       (scsw->cmd.stctl & SCSW_STCTL_STATUS_PEND) &&
>>> -	       (!(scsw->cmd.stctl & SCSW_STCTL_INTER_STATUS) ||
>>> -		  (scsw->cmd.actl & SCSW_ACTL_SUSPENDED));
>>> +	if (!scsw->tm.fctl)
>>> +		return 0;
>>> +	if (!(scsw->tm.stctl & SCSW_STCTL_STATUS_PEND))
>>> +		return 0;
>>> +	if (!(scsw->tm.stctl & SCSW_STCTL_INTER_STATUS))
>>> +		return 1;
>>> +	if (scsw->tm.actl & SCSW_ACTL_SUSPENDED)
>>> +		return 1;
>>> +	return 0;
>>>  }
> Here's the associated PoP text for this function (note: PNO=N)
>
> "The N bit is meaningful whenever the status-control field contains any
> of the indications listed below and at least one basic I/O function is
> also indicated at the subchannel:
> - Status pending with any combination of primary, secondary, or alert
>   status
> - Status pending alone
> - Status pending with intermediate status when the subchannel is also
>   suspended"
>
> Again a readable version could look like:
>
> /* Must indicate at least one I/O function. */
> if (!scsw->cmd.fctl)
>   return 0;
>
> /* Must be status pending. */
> if (!(scsw->cmd.stctl & SCSW_STCTL_STATUS_PEND))
>   return 0;
>
> /* Can be status pending alone, or with any combination of primary,
>  * secondary and alert => no intermediate status. */
> if (!(scsw->cmd.stctl & SCSW_STCTL_INTER_STATUS))
>   return 1;
>
> /* If intermediate, must be suspended. */
> if (scsw->cmd.actl & SCSW_ACTL_SUSPENDED)
>   return 1;
>
> return 0;
>
> The _tm_ functions below should be changed in the exact same way, while
> accessing the corresponding data fields in scsw->tm instead of scsw->cmd.
>
>>>  static inline int scsw_tm_is_valid_ectl(union scsw *scsw)
>>>  static inline int scsw_tm_is_valid_pno(union scsw *scsw)
> [1] https://www.ibm.com/support/pages/zarchitecture-principles-operation
>
Dear Peter Oberparleiter

Well done. Thank you for your kindly and professional explain what we need to do best.

-- 
Haowen Bai

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