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[198.48.202.89]) by smtp.gmail.com with ESMTPSA id x7sm1357406qtw.24.2021.07.29.08.56.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 29 Jul 2021 08:56:27 -0700 (PDT) Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Thu, 29 Jul 2021 11:56:26 -0400 Message-Id: From: "Liam Beguin" To: "Peter Rosin" , , , Cc: , , , Subject: Re: [PATCH v6 05/13] iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support References: <20210721030613.3105327-1-liambeguin@gmail.com> <20210721030613.3105327-6-liambeguin@gmail.com> <18f749be-284f-3342-a6d2-b42aa39fc13a@axentia.se> In-Reply-To: <18f749be-284f-3342-a6d2-b42aa39fc13a@axentia.se> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed Jul 28, 2021 at 3:19 AM EDT, Peter Rosin wrote: > On 2021-07-28 02:21, Liam Beguin wrote: > > On Fri Jul 23, 2021 at 5:16 PM EDT, Peter Rosin wrote: > >> On 2021-07-21 05:06, Liam Beguin wrote: > >>> From: Liam Beguin > >>> > >>> Some ADCs use IIO_VAL_INT_PLUS_{NANO,MICRO} scale types. > >>> Add support for these to allow using the iio-rescaler with them. > >>> > >>> Signed-off-by: Liam Beguin > >>> --- > >>> drivers/iio/afe/iio-rescale.c | 14 ++++++++++++++ > >>> 1 file changed, 14 insertions(+) > >>> > >>> diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-resc= ale.c > >>> index d0669fd8eac5..2b73047365cc 100644 > >>> --- a/drivers/iio/afe/iio-rescale.c > >>> +++ b/drivers/iio/afe/iio-rescale.c > >>> @@ -41,6 +41,20 @@ int rescale_process_scale(struct rescale *rescale,= int scale_type, > >>> do_div(tmp, 1000000000LL); > >>> *val =3D tmp; > >>> return scale_type; > >>> + case IIO_VAL_INT_PLUS_NANO: > >>> + tmp =3D ((s64)*val * 1000000000LL + *val2) * rescale->numerator; > >>> + tmp =3D div_s64(tmp, rescale->denominator); > >>> + > >>> + *val =3D div_s64(tmp, 1000000000LL); > >>> + *val2 =3D tmp - *val * 1000000000LL; > >>> + return scale_type; > >=20 > > Hi Peter, > >=20 > >> > >> Hi! > >> > >> My objection from v5 still stands. Did you forget or did you simply se= nd > >> the > >> wrong patch? > >=20 > > Apologies, again I didn't mean to make it seem like I ignored your comm= ents. > > I tried your suggestion, but had issues when *val2 would overflow into > > the integer part. Hi Peter, > > Not saying anything about it not working does indeed make it seem like > you > ignored it :-) Or did I just miss where you said this? Anyway, no > problem, > it can be a mess dealing with a string of commits when there are > numerous > things to take care of between each iteration. And it's very easy to > burn > out and just back away. Please don't do that! It was my mistake. Thanks for the encouragement :-) > > > Even though what I has was more prone to integer overflow with the firs= t > > multiplication, I thought it was still a valid solution as it passed th= e > > tests. > > I did state that you'd need to add overflow handling from the fraction > calculation and handling for negative values, so it was no surprise that > my original sketchy suggestion didn't work as-is. > > >=20 > >> > >> Untested suggestion, this time handling negative values and > >> canonicalizing any > >> overflow from the fraction calculation. > >> > >> neg =3D *val < 0 || *val2 < 0; > >> tmp =3D (s64)abs(*val) * rescale->numerator; > >> rem =3D do_div(tmp, rescale->denominator); > >> *val =3D tmp; > >> tmp =3D rem * 1000000000LL + (s64)abs(*val2) * rescale->numerator; > >> do_div(tmp, rescale->denominator); > >> *val2 =3D do_div(tmp, 1000000000LL); > >> *val +=3D tmp; > >> if (neg) { > >> if (*val < 0) > >> *val =3D -*val; > >> else > >> *val2 =3D -*val; > > This last line should of course be *val2 =3D -*val2; > Sorry. > > >=20 > > I'll look into this suggestion. > > Thanks! > Starting from what you suggested, here's what I came up with. I also added a few test cases to cover corner cases. if (scale_type =3D=3D IIO_VAL_INT_PLUS_NANO) mult =3D 1000000000LL; else mult =3D 1000000LL; /* * For IIO_VAL_INT_PLUS_{MICRO,NANO} scale types if *val OR * *val2 is negative the schan scale is negative */ neg =3D *val < 0 || *val2 < 0; tmp =3D (s64)abs(*val) * (s32)abs(rescale->numerator); *val =3D div_s64_rem(tmp, (s32)abs(rescale->denominator), &rem); tmp =3D (s64)rem * mult + (s64)abs(*val2) * (s32)abs(rescale->numerator); tmp =3D div_s64(tmp, (s32)abs(rescale->denominator)); *val +=3D div_s64_rem(tmp, mult, val2); /* * If the schan scale or only one of the rescaler elements is * negative, the combined scale is negative. */ if (neg || ((rescale->numerator < 0) ^ (rescale->denominator < 0))) *val =3D -*val; return scale_type; > >=20 > >> } > >> > >>> + case IIO_VAL_INT_PLUS_MICRO: > >>> + tmp =3D ((s64)*val * 1000000LL + *val2) * rescale->numerator; > >>> + tmp =3D div_s64(tmp, rescale->denominator); > >>> + > >>> + *val =3D div_s64(tmp, 1000000); > >> > >> Why do you not have the LL suffix here? > >=20 > > Doesnt' LL make it into a 64 bit integer? > > I left it out because the second parameter of div_s64() should be s32. > > It just looked really odd with 1000000000LL for all instances, but then > 1000000LL only for some. The lack of symmetry bothered me. > > To me, it seems as if we either need to support old/small crap with > int being 16-bit, or we don't. If we don't need support for 16-bit, > then we don't need any LL suffix, since 1000000000 fits just fine in > 32-bit. If we do need 16-bit support, then we need LL (or something) > all over since neither 1000000 nor 1000000000 fit in 16-bit. > > I think the compiler looks at the value of the constant and not the > size of its type when selecting how big values the mul/add/whatever > needs handle. So, adding LL feels like the safe option. Further, I > guesstimate that the runtime cost of adding LL is zero and that the > compile time cost is negligible. Thanks for the explanation, I thought it might matter but I agree that the asymmetry looks odd. I'll fix it. Thanks, Liam > > But maybe I'm missing something? > > Cheers, > Peter > > >=20 > > Thanks, > > Liam > >=20 > >> > >> Cheers, > >> Peter > >> > >>> + *val2 =3D tmp - *val * 1000000; > >>> + return scale_type; > >>> default: > >>> return -EOPNOTSUPP; > >>> } > >>> > >=20