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([2600:8803:e7e4:500:732:592e:7567:cf3f]) by smtp.gmail.com with ESMTPSA id 006d021491bc7-67e2308f212sm6785607eaf.6.2026.03.31.07.01.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 31 Mar 2026 07:01:39 -0700 (PDT) Message-ID: Date: Tue, 31 Mar 2026 09:01:38 -0500 Precedence: bulk X-Mailing-List: linux-iio@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] iio: adc: ad4695: Fix call ordering in offload buffer postenable To: radu.sabau@analog.com, Lars-Peter Clausen , Michael Hennerich , =?UTF-8?Q?Nuno_S=C3=A1?= , Jonathan Cameron , Andy Shevchenko Cc: linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260330-ad4696-fix-v1-1-e841e96451b2@analog.com> Content-Language: en-US From: David Lechner In-Reply-To: <20260330-ad4696-fix-v1-1-e841e96451b2@analog.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/30/26 8:34 AM, Radu Sabau via B4 Relay wrote: > From: Radu Sabau > > ad4695_enter_advanced_sequencer_mode() was called after > spi_offload_trigger_enable(), meaning a regular SPI transfer could be in > flight while the offload was already active. When the offload fires its > completion interrupt concurrently with the regular transfer, the SPI > engine interrupt handler is not designed to handle both at once, leading > to a kernel panic. > > Fix this by calling ad4695_enter_advanced_sequencer_mode() before > spi_offload_trigger_enable(), ensuring all SPI bus accesses are complete > before the offload becomes active. This is consistent with the same > constraint that already applies to the BUSY_GP_EN write above it. > > Update the error unwind labels accordingly: add err_exit_conversion_mode > so that a failure of spi_offload_trigger_enable() correctly exits > conversion mode before clearing BUSY_GP_EN. > > Fixes: f09f140e3ea8 ("iio: adc: ad4695: Add support for SPI offload") > Signed-off-by: Radu Sabau > --- > When enabling the IIO buffer for SPI offload operation on AD4695/AD4696, > ad4695_enter_advanced_sequencer_mode() was called after > spi_offload_trigger_enable(), resulting in a regular SPI transfer being > in flight while the offload was already active. This caused a kernel > panic in the SPI engine interrupt handler. > > This series fixes the call ordering so all SPI bus accesses complete > before the offload becomes active, consistent with the constraint that > was already documented for the BUSY_GP_EN write in the same function. > --- > drivers/iio/adc/ad4695.c | 31 ++++++++++++++----------------- > 1 file changed, 14 insertions(+), 17 deletions(-) > > diff --git a/drivers/iio/adc/ad4695.c b/drivers/iio/adc/ad4695.c > index cda419638d9a..c6721f5ac8af 100644 > --- a/drivers/iio/adc/ad4695.c > +++ b/drivers/iio/adc/ad4695.c > @@ -866,24 +866,24 @@ static int ad4695_offload_buffer_postenable(struct iio_dev *indio_dev) > return ret; > > /* > - * NB: technically, this is part the SPI offload trigger enable, but it > - * doesn't work to call it from the offload trigger enable callback > - * because it requires accessing the SPI bus. Calling it from the > - * trigger enable callback could cause a deadlock. > + * NB: these are technically part of the SPI offload trigger enable, but > + * they can't be called from the offload trigger enable callback because > + * they require accessing the SPI bus. Calling them from the trigger > + * enable callback could cause a deadlock. I didn't see a explanation for changing the comment here. I think "this" is still correct instead of "these" because only the BUSY pin is the trigger, so only the one regmap_set_bits() below would be in the trigger callback if it was possible. If we want to improve the comment to make it more clear, I would save that for a separate patch and specifically mention the BUSY output. > */ > ret = regmap_set_bits(st->regmap, AD4695_REG_GP_MODE, > AD4695_REG_GP_MODE_BUSY_GP_EN); > if (ret) > goto err_unoptimize_message; > > - ret = spi_offload_trigger_enable(st->offload, st->offload_trigger, > - &config); > + ret = ad4695_enter_advanced_sequencer_mode(st, num_slots); > if (ret) > goto err_disable_busy_output; > > - ret = ad4695_enter_advanced_sequencer_mode(st, num_slots); > + ret = spi_offload_trigger_enable(st->offload, st->offload_trigger, > + &config); > if (ret) > - goto err_offload_trigger_disable; > + goto err_exit_conversion_mode; > > mutex_lock(&st->cnv_pwm_lock); > pwm_get_state(st->cnv_pwm, &state); > @@ -895,22 +895,19 @@ static int ad4695_offload_buffer_postenable(struct iio_dev *indio_dev) > ret = pwm_apply_might_sleep(st->cnv_pwm, &state); > mutex_unlock(&st->cnv_pwm_lock); > if (ret) > - goto err_offload_exit_conversion_mode; > + goto err_trigger_disable; > > return 0; > > -err_offload_exit_conversion_mode: > +err_trigger_disable: > /* > - * We have to unwind in a different order to avoid triggering offload. > - * ad4695_exit_conversion_mode() triggers a conversion, so it has to be > - * done after spi_offload_trigger_disable(). > + * ad4695_exit_conversion_mode() triggers a conversion, so the offload > + * must be disabled first to avoid capturing a spurious sample. Since this becomes the natural unwinding order, I don't think we need the comment at all any more. There is still a similar comment in ad4695_offload_buffer_predisable() so we aren't losing this information if we remove it here. > */ > spi_offload_trigger_disable(st->offload, st->offload_trigger); > - ad4695_exit_conversion_mode(st); > - goto err_disable_busy_output; > > -err_offload_trigger_disable: > - spi_offload_trigger_disable(st->offload, st->offload_trigger); > +err_exit_conversion_mode: > + ad4695_exit_conversion_mode(st); > > err_disable_busy_output: > regmap_clear_bits(st->regmap, AD4695_REG_GP_MODE, > > --- > base-commit: 11439c4635edd669ae435eec308f4ab8a0804808 > change-id: 20260330-ad4696-fix-186955a8c511 > > Best regards,