[PATCH v2 2/2] iio: adc: stm32-adc: fix a race when using several adcs with dma and irq

[Fabrice Gasnier]

End of conversion may be handled by using IRQ or DMA. There may be a
race when two conversions complete at the same time on several ADCs.
EOC can be read as 'set' for several ADCs, with:
- an ADC configured to use IRQs. EOCIE bit is set. The handler is normally
  called in this case.
- an ADC configured to use DMA. EOCIE bit isn't set. EOC triggers the DMA
  request instead. It's then automatically cleared by DMA read. But the
  handler gets called due to status bit is temporarily set (IRQ triggered
  by the other ADC).
So both EOC status bit in CSR and EOCIE control bit must be checked
before invoking the interrupt handler (e.g. call ISR only for
IRQ-enabled ADCs).

Fixes: 2763ea0585c9 ("iio: adc: stm32: add optional dma support")

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@xxxxxx>
---
Changes in v2:
- Keep registers definitions as a whole block to ease readability (add
  a precursor patch to move them to header file)
---
 drivers/iio/adc/stm32-adc-core.c | 43 +++++++++++++++++++++++++++++++++++++---
 drivers/iio/adc/stm32-adc-core.h |  1 +
 2 files changed, 41 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/adc/stm32-adc-core.c b/drivers/iio/adc/stm32-adc-core.c
index 84ac326..93a096a 100644
--- a/drivers/iio/adc/stm32-adc-core.c
+++ b/drivers/iio/adc/stm32-adc-core.c
@@ -44,6 +44,8 @@
  * @eoc1:	adc1 end of conversion flag in @csr
  * @eoc2:	adc2 end of conversion flag in @csr
  * @eoc3:	adc3 end of conversion flag in @csr
+ * @ier:	interrupt enable register offset for each adc
+ * @eocie_msk:	end of conversion interrupt enable mask in @ier
  */
 struct stm32_adc_common_regs {
 	u32 csr;
@@ -51,6 +53,8 @@ struct stm32_adc_common_regs {
 	u32 eoc1_msk;
 	u32 eoc2_msk;
 	u32 eoc3_msk;
+	u32 ier;
+	u32 eocie_msk;
 };
 
 struct stm32_adc_priv;
@@ -276,6 +280,8 @@ static const struct stm32_adc_common_regs stm32f4_adc_common_regs = {
 	.eoc1_msk = STM32F4_EOC1,
 	.eoc2_msk = STM32F4_EOC2,
 	.eoc3_msk = STM32F4_EOC3,
+	.ier = STM32F4_ADC_CR1,
+	.eocie_msk = STM32F4_EOCIE,
 };
 
 /* STM32H7 common registers definitions */
@@ -284,8 +290,24 @@ static const struct stm32_adc_common_regs stm32h7_adc_common_regs = {
 	.ccr = STM32H7_ADC_CCR,
 	.eoc1_msk = STM32H7_EOC_MST,
 	.eoc2_msk = STM32H7_EOC_SLV,
+	.ier = STM32H7_ADC_IER,
+	.eocie_msk = STM32H7_EOCIE,
 };
 
+static const unsigned int stm32_adc_offset[STM32_ADC_MAX_ADCS] = {
+	0, STM32_ADC_OFFSET, STM32_ADC_OFFSET * 2,
+};
+
+static unsigned int stm32_adc_eoc_enabled(struct stm32_adc_priv *priv,
+					  unsigned int adc)
+{
+	u32 ier, offset = stm32_adc_offset[adc];
+
+	ier = readl_relaxed(priv->common.base + offset + priv->cfg->regs->ier);
+
+	return ier & priv->cfg->regs->eocie_msk;
+}
+
 /* ADC common interrupt for all instances */
 static void stm32_adc_irq_handler(struct irq_desc *desc)
 {
@@ -296,13 +318,28 @@ static void stm32_adc_irq_handler(struct irq_desc *desc)
 	chained_irq_enter(chip, desc);
 	status = readl_relaxed(priv->common.base + priv->cfg->regs->csr);
 
-	if (status & priv->cfg->regs->eoc1_msk)
+	/*
+	 * End of conversion may be handled by using IRQ or DMA. There may be a
+	 * race here when two conversions complete at the same time on several
+	 * ADCs. EOC may be read 'set' for several ADCs, with:
+	 * - an ADC configured to use DMA (EOC triggers the DMA request, and
+	 *   is then automatically cleared by DR read in hardware)
+	 * - an ADC configured to use IRQs (EOCIE bit is set. The handler must
+	 *   be called in this case)
+	 * So both EOC status bit in CSR and EOCIE control bit must be checked
+	 * before invoking the interrupt handler (e.g. call ISR only for
+	 * IRQ-enabled ADCs).
+	 */
+	if (status & priv->cfg->regs->eoc1_msk &&
+	    stm32_adc_eoc_enabled(priv, 0))
 		generic_handle_irq(irq_find_mapping(priv->domain, 0));
 
-	if (status & priv->cfg->regs->eoc2_msk)
+	if (status & priv->cfg->regs->eoc2_msk &&
+	    stm32_adc_eoc_enabled(priv, 1))
 		generic_handle_irq(irq_find_mapping(priv->domain, 1));
 
-	if (status & priv->cfg->regs->eoc3_msk)
+	if (status & priv->cfg->regs->eoc3_msk &&
+	    stm32_adc_eoc_enabled(priv, 2))
 		generic_handle_irq(irq_find_mapping(priv->domain, 2));
 
 	chained_irq_exit(chip, desc);
diff --git a/drivers/iio/adc/stm32-adc-core.h b/drivers/iio/adc/stm32-adc-core.h
index 94aa2d2..2579d51 100644
--- a/drivers/iio/adc/stm32-adc-core.h
+++ b/drivers/iio/adc/stm32-adc-core.h
@@ -25,6 +25,7 @@
  * --------------------------------------------------------
  */
 #define STM32_ADC_MAX_ADCS		3
+#define STM32_ADC_OFFSET		0x100
 #define STM32_ADCX_COMN_OFFSET		0x300
 
 /* STM32F4 - Registers for each ADC instance */
-- 
2.7.4