From: Haibo Chen haibo.chen@nxp.com
[ Upstream commit 12c9b09e981ab14ebec8e4eefa946cbd26dd306b ]
ADC calibration might fail because of the noise on reference voltage. To avoid calibration fail, need to meet the following requirement: ADC reference voltage Noise < 1.8V * 1/2^ENOB
For the case which the ADC reference voltage on board do not meet the requirement, still load the calibrated values, so ADC can also work but maybe not that accurate.
Signed-off-by: Haibo Chen haibo.chen@nxp.com Reviewed-by: Frank Li Frank.Li@nxp.com Reviewed-by: Primoz Fiser primoz.fiser@norik.com Link: https://patch.msgid.link/20250812-adc-v2-2-0260833f13b8@nxp.com Signed-off-by: Jonathan Cameron Jonathan.Cameron@huawei.com Signed-off-by: Sasha Levin sashal@kernel.org ---
LLM Generated explanations, may be completely bogus:
YES
Explanation - Problem addressed: On some boards the i.MX93 ADC calibration fails due to reference voltage noise (commit message). In the current code, a calibration failure aborts driver probe, leaving the ADC unusable for users. - Current failure path: `imx93_adc_calibration()` returns `-EAGAIN` on calibration failure, explicitly powering down the ADC and aborting probe: - Failure check/return: drivers/iio/adc/imx93_adc.c:181 (checks `IMX93_ADC_MSR_CALFAIL_MASK`) and drivers/iio/adc/imx93_adc.c:185 (returns `-EAGAIN`). - Probe abort on error: drivers/iio/adc/imx93_adc.c:367 (calibration call) and drivers/iio/adc/imx93_adc.c:368–396 (error unwinding). - What the patch changes: - Adds `IMX93_ADC_CALCFG0` (0x3A0) and `IMX93_ADC_CALCFG0_LDFAIL_MASK` (BIT(4)) so the driver can instruct hardware to load calibrated values even if calibration “fails”. - In `imx93_adc_calibration()` (drivers/iio/adc/imx93_adc.c:146), before starting calibration, it writes `IMX93_ADC_CALCFG0_LDFAIL_MASK` to `IMX93_ADC_CALCFG0` to enable “load-on-fail”. - It changes the failure handling on `CALFAIL`: instead of returning `-EAGAIN`, it logs a warning and continues, allowing the driver to register and the ADC to function, albeit with potentially reduced accuracy. - The timeout path remains unchanged and still returns an error if calibration never completes (drivers/iio/adc/imx93_adc.c:171–178), preserving safety for a hard failure. - User impact: This is a practical fix for real boards where Vref noise is above the stated threshold; without it, the ADC never comes up. With it, the ADC works (possibly with lower accuracy), which is typically preferable to complete unavailability. - Scope and risk: - Small, contained change in a single driver (`drivers/iio/adc/imx93_adc.c`) with no ABI or framework changes. - No architectural refactoring; only adds a register define and a single bit write plus relaxed error handling. - Timeout/hard-error behavior is unchanged; only soft failure (CALFAIL) behavior is relaxed. - The driver matches only `nxp,imx93-adc` (drivers/iio/adc/imx93_adc.c:465–469), so the change is isolated to this hardware. - Stable criteria: - Fixes a user-visible bug (driver failing to probe on noisy Vref boards). - Minimal and low risk; confined to probe/calibration logic. - No new features; behavior change is a robustness fix with guarded warning. - No broader side effects beyond this ADC device.
Given these points, this is a solid candidate for backporting to any stable trees that contain the i.MX93 ADC driver and its current fail- hard calibration path.
drivers/iio/adc/imx93_adc.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-)
diff --git a/drivers/iio/adc/imx93_adc.c b/drivers/iio/adc/imx93_adc.c index 7feaafd2316f2..9f1546c3d39d5 100644 --- a/drivers/iio/adc/imx93_adc.c +++ b/drivers/iio/adc/imx93_adc.c @@ -38,6 +38,7 @@ #define IMX93_ADC_PCDR6 0x118 #define IMX93_ADC_PCDR7 0x11c #define IMX93_ADC_CALSTAT 0x39C +#define IMX93_ADC_CALCFG0 0x3A0
/* ADC bit shift */ #define IMX93_ADC_MCR_MODE_MASK BIT(29) @@ -58,6 +59,8 @@ #define IMX93_ADC_IMR_ECH_MASK BIT(0) #define IMX93_ADC_PCDR_CDATA_MASK GENMASK(11, 0)
+#define IMX93_ADC_CALCFG0_LDFAIL_MASK BIT(4) + /* ADC status */ #define IMX93_ADC_MSR_ADCSTATUS_IDLE 0 #define IMX93_ADC_MSR_ADCSTATUS_POWER_DOWN 1 @@ -145,7 +148,7 @@ static void imx93_adc_config_ad_clk(struct imx93_adc *adc)
static int imx93_adc_calibration(struct imx93_adc *adc) { - u32 mcr, msr; + u32 mcr, msr, calcfg; int ret;
/* make sure ADC in power down mode */ @@ -158,6 +161,11 @@ static int imx93_adc_calibration(struct imx93_adc *adc)
imx93_adc_power_up(adc);
+ /* Enable loading of calibrated values even in fail condition */ + calcfg = readl(adc->regs + IMX93_ADC_CALCFG0); + calcfg |= IMX93_ADC_CALCFG0_LDFAIL_MASK; + writel(calcfg, adc->regs + IMX93_ADC_CALCFG0); + /* * TODO: we use the default TSAMP/NRSMPL/AVGEN in MCR, * can add the setting of these bit if need in future. @@ -180,9 +188,13 @@ static int imx93_adc_calibration(struct imx93_adc *adc) /* check whether calbration is success or not */ msr = readl(adc->regs + IMX93_ADC_MSR); if (msr & IMX93_ADC_MSR_CALFAIL_MASK) { + /* + * Only give warning here, this means the noise of the + * reference voltage do not meet the requirement: + * ADC reference voltage Noise < 1.8V * 1/2^ENOB + * And the resault of ADC is not that accurate. + */ dev_warn(adc->dev, "ADC calibration failed!\n"); - imx93_adc_power_down(adc); - return -EAGAIN; }
return 0;