drm/amd/display: fix sporadic multiple aux transaction failure

[why]
When there are multiple aux transaction in parallel, it is sometime
sporadically the aux transaction starts to continuously fail. The
aux transaction was failing because the busy bit for the given gpio
pin was always set. The busy bit was alway set because the
programming sequence to read, modify and write busy bit was not
atomic. Due to which when multiple threads are trying to modify the
busy bits for their gpio pins in the same integer variable sometimes
the busy bits integer variable is written with old data causing
failure.

[how]
Instead of using individual bits to track gpio pins and grouping
them to integers, one byte will be allcoated for each gpio pin.
Now whenever a gpio pin needs to be set to mark being used, only
writing a value of one to that byte is sufficient, other bytes
are not impacted. Also no need to have atomicity with bytes unlike
with bits.
Signed-off-by: Yogesh Mohan Marimuthu <yogesh.mohanmarimuthu@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/gpio/gpio_service.c

@@ -56,7 +56,6 @@ struct gpio_service *dal_gpio_service_create(
 	struct dc_context *ctx)
 {
 	struct gpio_service *service;
-
 	uint32_t index_of_id;
 
 	service = kzalloc(sizeof(struct gpio_service), GFP_KERNEL);
@@ -78,44 +77,33 @@ struct gpio_service *dal_gpio_service_create(
 		goto failure_1;
 	}
 
-	/* allocate and initialize business storage */
+	/* allocate and initialize busyness storage */
 	{
-		const uint32_t bits_per_uint = sizeof(uint32_t) << 3;
-
 		index_of_id = 0;
 		service->ctx = ctx;
 
 		do {
 			uint32_t number_of_bits =
 				service->factory.number_of_pins[index_of_id];
+			uint32_t i = 0;
 
-			uint32_t number_of_uints =
-				(number_of_bits + bits_per_uint - 1) /
-				bits_per_uint;
-
-			uint32_t *slot;
-
-			if (number_of_bits) {
-				uint32_t index_of_uint = 0;
+			if (number_of_bits)  {
+				service->busyness[index_of_id] =
+					kcalloc(number_of_bits, sizeof(char),
+						GFP_KERNEL);
 
-				slot = kcalloc(number_of_uints,
-					       sizeof(uint32_t),
-					       GFP_KERNEL);
-
-				if (!slot) {
+				if (!service->busyness[index_of_id]) {
 					BREAK_TO_DEBUGGER();
 					goto failure_2;
 				}
 
 				do {
-					slot[index_of_uint] = 0;
-
-					++index_of_uint;
-				} while (index_of_uint < number_of_uints);
-			} else
-				slot = NULL;
-
-			service->busyness[index_of_id] = slot;
+					service->busyness[index_of_id][i] = 0;
+					++i;
+				} while (i < number_of_bits);
+			} else {
+				service->busyness[index_of_id] = NULL;
+			}
 
 			++index_of_id;
 		} while (index_of_id < GPIO_ID_COUNT);
@@ -125,13 +113,8 @@ struct gpio_service *dal_gpio_service_create(
 
 failure_2:
 	while (index_of_id) {
-		uint32_t *slot;
-
 		--index_of_id;
-
-		slot = service->busyness[index_of_id];
-
-		kfree(slot);
+		kfree(service->busyness[index_of_id]);
 	}
 
 failure_1:
@@ -169,9 +152,7 @@ void dal_gpio_service_destroy(
 		uint32_t index_of_id = 0;
 
 		do {
-			uint32_t *slot = (*ptr)->busyness[index_of_id];
-
-			kfree(slot);
+			kfree((*ptr)->busyness[index_of_id]);
 
 			++index_of_id;
 		} while (index_of_id < GPIO_ID_COUNT);
@@ -192,11 +173,7 @@ static bool is_pin_busy(
 	enum gpio_id id,
 	uint32_t en)
 {
-	const uint32_t bits_per_uint = sizeof(uint32_t) << 3;
-
-	const uint32_t *slot = service->busyness[id] + (en / bits_per_uint);
-
-	return 0 != (*slot & (1 << (en % bits_per_uint)));
+	return service->busyness[id][en];
 }
 
 static void set_pin_busy(
@@ -204,10 +181,7 @@ static void set_pin_busy(
 	enum gpio_id id,
 	uint32_t en)
 {
-	const uint32_t bits_per_uint = sizeof(uint32_t) << 3;
-
-	service->busyness[id][en / bits_per_uint] |=
-		(1 << (en % bits_per_uint));
+	service->busyness[id][en] = true;
 }
 
 static void set_pin_free(
@@ -215,10 +189,7 @@ static void set_pin_free(
 	enum gpio_id id,
 	uint32_t en)
 {
-	const uint32_t bits_per_uint = sizeof(uint32_t) << 3;
-
-	service->busyness[id][en / bits_per_uint] &=
-		~(1 << (en % bits_per_uint));
+	service->busyness[id][en] = false;
 }
 
 enum gpio_result dal_gpio_service_open(

drivers/gpu/drm/amd/display/dc/gpio/gpio_service.h

@@ -36,10 +36,9 @@ struct gpio_service {
 	/*
 	 * @brief
 	 * Business storage.
-	 * For each member of 'enum gpio_id',
-	 * store array of bits (packed into uint32_t slots),
-	 * index individual bit by 'en' value */
-	uint32_t *busyness[GPIO_ID_COUNT];
+	 * one byte For each member of 'enum gpio_id'
+	 */
+	char *busyness[GPIO_ID_COUNT];
 };
 
 enum gpio_result dal_gpio_service_open(