| Message ID | 20230127125714.44608-1-ian.ray@ge.com (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
| Series | drivers: iio: adc: ltc2497: fix LSB shift | expand |
On Fri, 27 Jan 2023 14:57:14 +0200 Ian Ray <ian.ray@ge.com> wrote: > Correct the "sub_lsb" shift for both ltc2497 and ltc2499. Hi Iain, Thanks for the patch. > > An earlier version of the code shifted by 14 but this was a consequence > of reading three bytes into a __be32 buffer and using be32_to_cpu(), so > eight extra bits needed to be skipped. Now we use get_unaligned_be24() > and thus the additional skip is wrong. > > Fixes 2187cfe ("drivers: iio: adc: ltc2497: LTC2499 support") This isn't in standard Fixes tag format. If nothing else comes up I'll fix up whilst applying. > Signed-off-by: Ian Ray <ian.ray@ge.com> > --- > drivers/iio/adc/ltc2497.c | 6 ++---- > 1 file changed, 2 insertions(+), 4 deletions(-) > > diff --git a/drivers/iio/adc/ltc2497.c b/drivers/iio/adc/ltc2497.c > index 17370c5..ec198c6 100644 > --- a/drivers/iio/adc/ltc2497.c > +++ b/drivers/iio/adc/ltc2497.c > @@ -28,7 +28,6 @@ struct ltc2497_driverdata { > struct ltc2497core_driverdata common_ddata; > struct i2c_client *client; > u32 recv_size; > - u32 sub_lsb; > /* > * DMA (thus cache coherency maintenance) may require the > * transfer buffers to live in their own cache lines. > @@ -65,10 +64,10 @@ static int ltc2497_result_and_measure(struct ltc2497core_driverdata *ddata, > * equivalent to a sign extension. > */ > if (st->recv_size == 3) { > - *val = (get_unaligned_be24(st->data.d8) >> st->sub_lsb) > + *val = (get_unaligned_be24(st->data.d8) >> 6) > - BIT(ddata->chip_info->resolution + 1); > } else { > - *val = (be32_to_cpu(st->data.d32) >> st->sub_lsb) > + *val = (be32_to_cpu(st->data.d32) >> 6) > - BIT(ddata->chip_info->resolution + 1); > } > > @@ -122,7 +121,6 @@ static int ltc2497_probe(struct i2c_client *client) > st->common_ddata.chip_info = chip_info; > > resolution = chip_info->resolution; > - st->sub_lsb = 31 - (resolution + 1); > st->recv_size = BITS_TO_BYTES(resolution) + 1; > > return ltc2497core_probe(dev, indio_dev);
On Fri, 27 Jan 2023 17:47:56 +0000 Jonathan Cameron <Jonathan.Cameron@Huawei.com> wrote: > On Fri, 27 Jan 2023 14:57:14 +0200 > Ian Ray <ian.ray@ge.com> wrote: > > > Correct the "sub_lsb" shift for both ltc2497 and ltc2499. I dropped the ltc2499 mention here as that one seems to be unaffected by this patch (beyond as a simplification) > > Hi Iain, Thanks for the patch. > > > > > An earlier version of the code shifted by 14 but this was a consequence > > of reading three bytes into a __be32 buffer and using be32_to_cpu(), so > > eight extra bits needed to be skipped. Now we use get_unaligned_be24() > > and thus the additional skip is wrong. > > > > Fixes 2187cfe ("drivers: iio: adc: ltc2497: LTC2499 support") > > This isn't in standard Fixes tag format. If nothing else comes > up I'll fix up whilst applying. > > > Signed-off-by: Ian Ray <ian.ray@ge.com> Fix looks good to me. (I noted my reasoning below on basis someone might find it useful) Applied to the fixes-togreg branch of iio.git with fixes tag fixed and marked for stable. Please take a look at: https://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git/commit/?h=fixes-togreg&id=6327a930ab7bfa1ab33bcdffd5f5f4b1e7131504 to check I didn't mess anything up. Thanks, Jonathan > > --- > > drivers/iio/adc/ltc2497.c | 6 ++---- > > 1 file changed, 2 insertions(+), 4 deletions(-) > > > > diff --git a/drivers/iio/adc/ltc2497.c b/drivers/iio/adc/ltc2497.c > > index 17370c5..ec198c6 100644 > > --- a/drivers/iio/adc/ltc2497.c > > +++ b/drivers/iio/adc/ltc2497.c > > @@ -28,7 +28,6 @@ struct ltc2497_driverdata { > > struct ltc2497core_driverdata common_ddata; > > struct i2c_client *client; > > u32 recv_size; > > - u32 sub_lsb; > > /* > > * DMA (thus cache coherency maintenance) may require the > > * transfer buffers to live in their own cache lines. > > @@ -65,10 +64,10 @@ static int ltc2497_result_and_measure(struct ltc2497core_driverdata *ddata, > > * equivalent to a sign extension. > > */ > > if (st->recv_size == 3) { > > - *val = (get_unaligned_be24(st->data.d8) >> st->sub_lsb) > > + *val = (get_unaligned_be24(st->data.d8) >> 6) Prior to the buggy patch. 1) Read into top 3 bytes of BE32 which corresponds to 8 bits high. 2) Shift by 14. Before this patch 1) Read only 3 bytes 2) shift by (31 - (resolution + 1) where resolution is 16 so shift by 14. Indeed bug. After this patch. 1) Read 3 bytes 2) shift by 6 Matches original behaviour - fix is correct. > > - BIT(ddata->chip_info->resolution + 1); > > } else { > > - *val = (be32_to_cpu(st->data.d32) >> st->sub_lsb) > > + *val = (be32_to_cpu(st->data.d32) >> 6) Prior to this patch sub_lsb = 31 - (resolution + 1) where in this case resolution is 24 31 - 25 = 6 so this change is a noop change, so this is good. > > - BIT(ddata->chip_info->resolution + 1); > > } > > > > @@ -122,7 +121,6 @@ static int ltc2497_probe(struct i2c_client *client) > > st->common_ddata.chip_info = chip_info; > > > > resolution = chip_info->resolution; > > - st->sub_lsb = 31 - (resolution + 1); > > st->recv_size = BITS_TO_BYTES(resolution) + 1; > > > > return ltc2497core_probe(dev, indio_dev); >
On Sat, Jan 28, 2023 at 06:00:32PM +0000, Jonathan Cameron wrote: > > On Fri, 27 Jan 2023 17:47:56 +0000 > Jonathan Cameron <Jonathan.Cameron@Huawei.com> wrote: > > > On Fri, 27 Jan 2023 14:57:14 +0200 > > Ian Ray <ian.ray@ge.com> wrote: > > > > > Correct the "sub_lsb" shift for both ltc2497 and ltc2499. > > I dropped the ltc2499 mention here as that one seems to be unaffected > by this patch (beyond as a simplification) Makes sense. > > > > > Hi Iain, Thanks for the patch. > > > > > > > > An earlier version of the code shifted by 14 but this was a consequence > > > of reading three bytes into a __be32 buffer and using be32_to_cpu(), so > > > eight extra bits needed to be skipped. Now we use get_unaligned_be24() > > > and thus the additional skip is wrong. > > > > > > Fixes 2187cfe ("drivers: iio: adc: ltc2497: LTC2499 support") > > > > This isn't in standard Fixes tag format. If nothing else comes > > up I'll fix up whilst applying. > > > > > Signed-off-by: Ian Ray <ian.ray@ge.com> > > Fix looks good to me. (I noted my reasoning below on basis someone might > find it useful) > > Applied to the fixes-togreg branch of iio.git with fixes tag fixed and > marked for stable. > > Please take a look at: > https://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git/commit/?h=fixes-togreg&id=6327a930ab7bfa1ab33bcdffd5f5f4b1e7131504 > to check I didn't mess anything up. lgtm Many thanks! > > Thanks, > > Jonathan > > > > > --- > > > drivers/iio/adc/ltc2497.c | 6 ++---- > > > 1 file changed, 2 insertions(+), 4 deletions(-) > > > > > > diff --git a/drivers/iio/adc/ltc2497.c b/drivers/iio/adc/ltc2497.c > > > index 17370c5..ec198c6 100644 > > > --- a/drivers/iio/adc/ltc2497.c > > > +++ b/drivers/iio/adc/ltc2497.c > > > @@ -28,7 +28,6 @@ struct ltc2497_driverdata { > > > struct ltc2497core_driverdata common_ddata; > > > struct i2c_client *client; > > > u32 recv_size; > > > - u32 sub_lsb; > > > /* > > > * DMA (thus cache coherency maintenance) may require the > > > * transfer buffers to live in their own cache lines. > > > @@ -65,10 +64,10 @@ static int ltc2497_result_and_measure(struct ltc2497core_driverdata *ddata, > > > * equivalent to a sign extension. > > > */ > > > if (st->recv_size == 3) { > > > - *val = (get_unaligned_be24(st->data.d8) >> st->sub_lsb) > > > + *val = (get_unaligned_be24(st->data.d8) >> 6) > Prior to the buggy patch. > > 1) Read into top 3 bytes of BE32 which corresponds to 8 bits high. > 2) Shift by 14. > > Before this patch > 1) Read only 3 bytes > 2) shift by (31 - (resolution + 1) where resolution is 16 so shift by 14. > Indeed bug. > > After this patch. > 1) Read 3 bytes > 2) shift by 6 > > Matches original behaviour - fix is correct. > > > > > - BIT(ddata->chip_info->resolution + 1); > > > } else { > > > - *val = (be32_to_cpu(st->data.d32) >> st->sub_lsb) > > > + *val = (be32_to_cpu(st->data.d32) >> 6) > > Prior to this patch > sub_lsb = 31 - (resolution + 1) where in this case resolution is 24 > 31 - 25 = 6 so this change is a noop change, so this is good. > > > > - BIT(ddata->chip_info->resolution + 1); > > > } > > > > > > @@ -122,7 +121,6 @@ static int ltc2497_probe(struct i2c_client *client) > > > st->common_ddata.chip_info = chip_info; > > > > > > resolution = chip_info->resolution; > > > - st->sub_lsb = 31 - (resolution + 1); > > > st->recv_size = BITS_TO_BYTES(resolution) + 1; > > > > > > return ltc2497core_probe(dev, indio_dev); > > > >
diff --git a/drivers/iio/adc/ltc2497.c b/drivers/iio/adc/ltc2497.c index 17370c5..ec198c6 100644 --- a/drivers/iio/adc/ltc2497.c +++ b/drivers/iio/adc/ltc2497.c @@ -28,7 +28,6 @@ struct ltc2497_driverdata { struct ltc2497core_driverdata common_ddata; struct i2c_client *client; u32 recv_size; - u32 sub_lsb; /* * DMA (thus cache coherency maintenance) may require the * transfer buffers to live in their own cache lines. @@ -65,10 +64,10 @@ static int ltc2497_result_and_measure(struct ltc2497core_driverdata *ddata, * equivalent to a sign extension. */ if (st->recv_size == 3) { - *val = (get_unaligned_be24(st->data.d8) >> st->sub_lsb) + *val = (get_unaligned_be24(st->data.d8) >> 6) - BIT(ddata->chip_info->resolution + 1); } else { - *val = (be32_to_cpu(st->data.d32) >> st->sub_lsb) + *val = (be32_to_cpu(st->data.d32) >> 6) - BIT(ddata->chip_info->resolution + 1); } @@ -122,7 +121,6 @@ static int ltc2497_probe(struct i2c_client *client) st->common_ddata.chip_info = chip_info; resolution = chip_info->resolution; - st->sub_lsb = 31 - (resolution + 1); st->recv_size = BITS_TO_BYTES(resolution) + 1; return ltc2497core_probe(dev, indio_dev);
Correct the "sub_lsb" shift for both ltc2497 and ltc2499. An earlier version of the code shifted by 14 but this was a consequence of reading three bytes into a __be32 buffer and using be32_to_cpu(), so eight extra bits needed to be skipped. Now we use get_unaligned_be24() and thus the additional skip is wrong. Fixes 2187cfe ("drivers: iio: adc: ltc2497: LTC2499 support") Signed-off-by: Ian Ray <ian.ray@ge.com> --- drivers/iio/adc/ltc2497.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-)