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From: Cornelia Huck <cohuck@redhat.com>
To: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: David Hildenbrand <david@redhat.com>,
	Janosch Frank <frankja@linux.ibm.com>,
	kvm@vger.kernel.org, linux-s390@vger.kernel.org,
	thuth@redhat.com
Subject: Re: [kvm-unit-tests PATCH 2/4] lib: s390x: sclp: Extend feature probing
Date: Tue, 11 May 2021 18:36:22 +0200	[thread overview]
Message-ID: <20210511183622.1251155d.cohuck@redhat.com> (raw)
In-Reply-To: <20210511174645.550c741d@ibm-vm>

On Tue, 11 May 2021 17:46:45 +0200
Claudio Imbrenda <imbrenda@linux.ibm.com> wrote:

> On Tue, 11 May 2021 17:38:04 +0200
> David Hildenbrand <david@redhat.com> wrote:
> 
> > On 11.05.21 16:41, Claudio Imbrenda wrote:  
> > > On Tue, 11 May 2021 13:43:36 +0200
> > > David Hildenbrand <david@redhat.com> wrote:
> > >     
> > >> On 10.05.21 17:00, Janosch Frank wrote:    
> > >>> Lets grab more of the feature bits from SCLP read info so we can
> > >>> use them in the cpumodel tests.
> > >>>
> > >>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> > >>> Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> > >>> ---
> > >>>    lib/s390x/sclp.c | 20 ++++++++++++++++++++
> > >>>    lib/s390x/sclp.h | 38 +++++++++++++++++++++++++++++++++++---
> > >>>    2 files changed, 55 insertions(+), 3 deletions(-)
> > >>>
> > >>> diff --git a/lib/s390x/sclp.c b/lib/s390x/sclp.c
> > >>> index f11c2035..f25cfdb2 100644
> > >>> --- a/lib/s390x/sclp.c
> > >>> +++ b/lib/s390x/sclp.c
> > >>> @@ -129,6 +129,13 @@ CPUEntry *sclp_get_cpu_entries(void)
> > >>>    	return (CPUEntry *)(_read_info +
> > >>> read_info->offset_cpu); }
> > >>>    
> > >>> +static bool sclp_feat_check(int byte, int mask)
> > >>> +{
> > >>> +	uint8_t *rib = (uint8_t *)read_info;
> > >>> +
> > >>> +	return !!(rib[byte] & mask);
> > >>> +}    
> > >>
> > >> Instead of a mask, I'd just check for bit (offset) numbers within
> > >> the byte.
> > >>
> > >> static bool sclp_feat_check(int byte, int bit)
> > >> {
> > >> 	uint8_t *rib = (uint8_t *)read_info;
> > >>
> > >> 	return !!(rib[byte] & (0x80 >> bit));
> > >> }    
> > > 
> > > using a mask might be useful to check multiple facilities at the
> > > same time, but in that case the check should be    
> > 
> > IMHO checking with a mask here multiple facilities will be very error 
> > prone either way ... and we only have a single byte to check for.  
> 
> as I said, I do not have a strong opinion either way :)
> 
> 

If you need a tie breaker, I'd vote for bit over mask :)


  reply	other threads:[~2021-05-11 16:36 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-10 15:00 [kvm-unit-tests PATCH 0/4] s390x: cpumodel: Add sclp checks Janosch Frank
2021-05-10 15:00 ` [kvm-unit-tests PATCH 1/4] s390x: sclp: Only fetch read info byte 134 if cpu entries are above it Janosch Frank
2021-05-11 11:39   ` David Hildenbrand
2021-05-11 16:32   ` Cornelia Huck
2021-05-10 15:00 ` [kvm-unit-tests PATCH 2/4] lib: s390x: sclp: Extend feature probing Janosch Frank
2021-05-11 11:43   ` David Hildenbrand
2021-05-11 14:41     ` Claudio Imbrenda
2021-05-11 15:38       ` David Hildenbrand
2021-05-11 15:46         ` Claudio Imbrenda
2021-05-11 16:36           ` Cornelia Huck [this message]
2021-05-10 15:00 ` [kvm-unit-tests PATCH 3/4] s390x: cpumodel: FMT4 SCLP test Janosch Frank
2021-05-11 11:45   ` David Hildenbrand
2021-05-11 14:42   ` Claudio Imbrenda
2021-05-10 15:00 ` [kvm-unit-tests PATCH 4/4] s390x: cpumodel: FMT2 SCLP implies test Janosch Frank
2021-05-11 11:46   ` David Hildenbrand
2021-05-11 14:36   ` Claudio Imbrenda

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