[PATCH 05/18] drm/i915/gmbus: use generic read_poll_timeout*() instead of wait_for*()

[Jani Nikula]

Prefer generic poll helpers over i915 custom helpers.

The "two tier" wait_for_us() + wait_for() combination appeared without
much explanation in commit 4e6c2d58ba86 ("drm/i915: Take forcewake once
for the entire GMBUS transaction"). Try to mimic roughly the same with
the generic helpers.

wait_for_us() with 10 us or shorter timeouts ends up in
_wait_for_atomic(). Thus use read_poll_timeout_atomic() for the first
try, with the same 2 us timeout and no sleep.

For the fallback, the functional change is losing the exponentially
growing sleep of wait_for(), which used to be 10, 20, 40, ..., 640, and
1280 us. Use an arbitrary constant 500 us sleep instead. The timeout
remains at 50 ms.

Signed-off-by: Jani Nikula <jani.nikula at intel.com>
---
 drivers/gpu/drm/i915/display/intel_gmbus.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_gmbus.c b/drivers/gpu/drm/i915/display/intel_gmbus.c
index 0d73f32fe7f1..6cc82d196438 100644
--- a/drivers/gpu/drm/i915/display/intel_gmbus.c
+++ b/drivers/gpu/drm/i915/display/intel_gmbus.c
@@ -30,6 +30,7 @@
 #include <linux/export.h>
 #include <linux/i2c-algo-bit.h>
 #include <linux/i2c.h>
+#include <linux/iopoll.h>
 
 #include <drm/display/drm_hdcp_helper.h>
 
@@ -385,11 +386,17 @@ static int gmbus_wait(struct intel_display *display, u32 status, u32 irq_en)
 	intel_de_write_fw(display, GMBUS4(display), irq_en);
 
 	status |= GMBUS_SATOER;
-	ret = wait_for_us((gmbus2 = intel_de_read_fw(display, GMBUS2(display))) & status,
-			  2);
+
+	ret = read_poll_timeout_atomic(intel_de_read_fw, gmbus2,
+				       gmbus2 & status,
+				       0, 2, false,
+				       display, GMBUS2(display));
+
 	if (ret)
-		ret = wait_for((gmbus2 = intel_de_read_fw(display, GMBUS2(display))) & status,
-			       50);
+		ret = read_poll_timeout(intel_de_read_fw, gmbus2,
+					gmbus2 & status,
+					500, 50 * 1000, false,
+					display, GMBUS2(display));
 
 	intel_de_write_fw(display, GMBUS4(display), 0);
 	remove_wait_queue(&display->gmbus.wait_queue, &wait);
-- 
2.39.5