5.15-stable review patch. If anyone has any objections, please let me know.
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From: Uwe Kleine-König u.kleine-koenig@baylibre.com
[ Upstream commit 05a5d874f7327b75e9bc4359618017e047cc129c ]
Checking the binary representation of two structs (of the same type) for equality doesn't have the same semantic as comparing all members for equality. The former might find a difference where the latter doesn't in the presence of padding or when ambiguous types like float or bool are involved. (Floats typically have different representations for single values, like -0.0 vs +0.0, or 0.5 * 2² vs 0.25 * 2³. The type bool has at least 8 bits and the raw values 1 and 2 (probably) both evaluate to true, but memcmp finds a difference.)
When searching for a channel that already has the configuration we need, the comparison by member is the one that is needed.
Convert the comparison accordingly to compare the members one after another. Also add a static_assert guard to (somewhat) ensure that when struct ad7124_channel_config::config_props is expanded, the comparison is adapted, too.
This issue is somewhat theoretic, but using memcmp() on a struct is a bad pattern that is worth fixing.
Fixes: 7b8d045e497a ("iio: adc: ad7124: allow more than 8 channels") Signed-off-by: Uwe Kleine-König u.kleine-koenig@baylibre.com Link: https://patch.msgid.link/20250303114659.1672695-13-u.kleine-koenig@baylibre.... Signed-off-by: Jonathan Cameron Jonathan.Cameron@huawei.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/iio/adc/ad7124.c | 35 +++++++++++++++++++++++++++++++---- 1 file changed, 31 insertions(+), 4 deletions(-)
diff --git a/drivers/iio/adc/ad7124.c b/drivers/iio/adc/ad7124.c index 93f32bba73f62..31c8cb3bf811b 100644 --- a/drivers/iio/adc/ad7124.c +++ b/drivers/iio/adc/ad7124.c @@ -144,7 +144,11 @@ struct ad7124_chip_info { struct ad7124_channel_config { bool live; unsigned int cfg_slot; - /* Following fields are used to compare equality. */ + /* + * Following fields are used to compare for equality. If you + * make adaptations in it, you most likely also have to adapt + * ad7124_find_similar_live_cfg(), too. + */ struct_group(config_props, enum ad7124_ref_sel refsel; bool bipolar; @@ -331,15 +335,38 @@ static struct ad7124_channel_config *ad7124_find_similar_live_cfg(struct ad7124_ struct ad7124_channel_config *cfg) { struct ad7124_channel_config *cfg_aux; - ptrdiff_t cmp_size; int i;
- cmp_size = sizeof_field(struct ad7124_channel_config, config_props); + /* + * This is just to make sure that the comparison is adapted after + * struct ad7124_channel_config was changed. + */ + static_assert(sizeof_field(struct ad7124_channel_config, config_props) == + sizeof(struct { + enum ad7124_ref_sel refsel; + bool bipolar; + bool buf_positive; + bool buf_negative; + unsigned int vref_mv; + unsigned int pga_bits; + unsigned int odr; + unsigned int odr_sel_bits; + unsigned int filter_type; + })); + for (i = 0; i < st->num_channels; i++) { cfg_aux = &st->channels[i].cfg;
if (cfg_aux->live && - !memcmp(&cfg->config_props, &cfg_aux->config_props, cmp_size)) + cfg->refsel == cfg_aux->refsel && + cfg->bipolar == cfg_aux->bipolar && + cfg->buf_positive == cfg_aux->buf_positive && + cfg->buf_negative == cfg_aux->buf_negative && + cfg->vref_mv == cfg_aux->vref_mv && + cfg->pga_bits == cfg_aux->pga_bits && + cfg->odr == cfg_aux->odr && + cfg->odr_sel_bits == cfg_aux->odr_sel_bits && + cfg->filter_type == cfg_aux->filter_type) return cfg_aux; }