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SubjectRe: [PATCH v3 03/20] perf arm-spe: Refactor payload size calculation
Hi Andre,

On Fri, Oct 23, 2020 at 06:08:53PM +0100, André Przywara wrote:
> On 22/10/2020 15:57, Leo Yan wrote:
>
> Hi Leo,
>
> > This patch defines macro to extract "sz" field from header, and renames
> > the function payloadlen() to arm_spe_payload_len().
> >
> > Signed-off-by: Leo Yan <leo.yan@linaro.org>
> > ---
> > .../util/arm-spe-decoder/arm-spe-pkt-decoder.c | 18 +++++++++---------
> > .../util/arm-spe-decoder/arm-spe-pkt-decoder.h | 3 +++
> > 2 files changed, 12 insertions(+), 9 deletions(-)
> >
> > diff --git a/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c b/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c
> > index 7c7b5eb09fba..4294c133a465 100644
> > --- a/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c
> > +++ b/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c
> > @@ -69,22 +69,22 @@ const char *arm_spe_pkt_name(enum arm_spe_pkt_type type)
> > return arm_spe_packet_name[type];
> > }
> >
> > -/* return ARM SPE payload size from its encoding,
> > - * which is in bits 5:4 of the byte.
> > - * 00 : byte
> > - * 01 : halfword (2)
> > - * 10 : word (4)
> > - * 11 : doubleword (8)
> > +/*
> > + * Extracts the field "sz" from header bits and converts to bytes:
> > + * 00 : byte (1)
> > + * 01 : halfword (2)
> > + * 10 : word (4)
> > + * 11 : doubleword (8)
> > */
> > -static int payloadlen(unsigned char byte)
> > +static unsigned int arm_spe_payload_len(unsigned char hdr)
> > {
> > - return 1 << ((byte & 0x30) >> 4);
> > + return 1 << SPE_HEADER_SZ(hdr);
>
> I know, I know, I asked for this, but now looking again at it - and
> after having seen the whole series:
> This is now really trivial, and there are just two users? And
> SPE_HEADER_SZ() is only used in here?
>
> So either you just stuff the "1U << .." into the callers of
> arm_spe_payload_len(), or indeed put all of this into one macro (as you
> had originally).

Okay, will stuff the "1U << .." into the function.

> Apologies for this forth and back, but I didn't realise how this is
> really used eventually, and I just saw the transition from function to
> macro.

Actually you considered more than me and I learned many details from the
reivewing process, so no worries :)

> But please use 1U << .., signed shifts are treacherous.
>
> > }
> >
> > static int arm_spe_get_payload(const unsigned char *buf, size_t len,
> > struct arm_spe_pkt *packet)
> > {
> > - size_t payload_len = payloadlen(buf[0]);
> > + size_t payload_len = arm_spe_payload_len(buf[0]);
> >
> > if (len < 1 + payload_len)
> > return ARM_SPE_NEED_MORE_BYTES;
> > diff --git a/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.h b/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.h
> > index 4c870521b8eb..e9ea8e3ead5d 100644
> > --- a/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.h
> > +++ b/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.h
> > @@ -9,6 +9,7 @@
> >
> > #include <stddef.h>
> > #include <stdint.h>
> > +#include <linux/bits.h>
> >
> > #define ARM_SPE_PKT_DESC_MAX 256
> >
> > @@ -36,6 +37,8 @@ struct arm_spe_pkt {
> > uint64_t payload;
> > };
> >
> > +#define SPE_HEADER_SZ(val) ((val & GENMASK_ULL(5, 4)) >> 4)
>
> If you should keep this, please put parentheses around "val".

I went through your suggestions in this patch and other patches, looks
reasonable to me, will follow them and respin patch set.

Thanks a lot for timely reviewing!

Leo

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