[PATCH v4] drm: bridge: samsung-dsim: Fix waiting for empty cmd transfer FIFO on older Exynos

[Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>]

Samsung DSIM used in older Exynos SoCs (like Exynos 4210, 4x12, 3250)
doesn't report empty level of packer header FIFO. In case of those SoCs,
use the old way of waiting for empty command tranfsfer FIFO, removed
recently by commit 14806c641582 ("Drain command transfer FIFO before
transfer").

Fixes: 14806c641582 ("drm: bridge: samsung-dsim: Drain command transfer FIFO before transfer")
Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
---
v4:
- made has_broken_fifoctrl_emptyhdr a bitfield

v3:
- fixed 'fixes' tag, added reviewed-by

v2:
- added additional delay when workaround is used as suggested by Marek Vasut

v1: https://lore.kernel.org/all/20230718131859.3114135-1-m.szyprowski@xxxxxxxxxxx/
---

Samsung DSIM used in older Exynos SoCs (like Exynos 4210, 4x12, 3250)
doesn't report empty level of packer header FIFO. In case of those SoCs,
use the old way of waiting for empty command tranfsfer FIFO, removed
recently by commit 14806c641582 ("Drain command transfer FIFO before
transfer").

Fixes: 14806c641582 ("Drain command transfer FIFO before transfer")
Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
---
 drivers/gpu/drm/bridge/samsung-dsim.c | 18 ++++++++++++++++--
 include/drm/bridge/samsung-dsim.h     |  1 +
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
index c49091691ab1..35d29f6cd3e2 100644
--- a/drivers/gpu/drm/bridge/samsung-dsim.c
+++ b/drivers/gpu/drm/bridge/samsung-dsim.c
@@ -413,6 +413,7 @@ static const struct samsung_dsim_driver_data exynos3_dsi_driver_data = {
 	.m_min = 41,
 	.m_max = 125,
 	.min_freq = 500,
+	.has_broken_fifoctrl_emptyhdr = 1,
 };
 
 static const struct samsung_dsim_driver_data exynos4_dsi_driver_data = {
@@ -429,6 +430,7 @@ static const struct samsung_dsim_driver_data exynos4_dsi_driver_data = {
 	.m_min = 41,
 	.m_max = 125,
 	.min_freq = 500,
+	.has_broken_fifoctrl_emptyhdr = 1,
 };
 
 static const struct samsung_dsim_driver_data exynos5_dsi_driver_data = {
@@ -1010,8 +1012,20 @@ static int samsung_dsim_wait_for_hdr_fifo(struct samsung_dsim *dsi)
 	do {
 		u32 reg = samsung_dsim_read(dsi, DSIM_FIFOCTRL_REG);
 
-		if (reg & DSIM_SFR_HEADER_EMPTY)
-			return 0;
+		if (!dsi->driver_data->has_broken_fifoctrl_emptyhdr) {
+			if (reg & DSIM_SFR_HEADER_EMPTY)
+				return 0;
+		} else {
+			if (!(reg & DSIM_SFR_HEADER_FULL)) {
+				/*
+				 * Wait a little bit, so the pending data can
+				 * actually leave the FIFO to avoid overflow.
+				 */
+				if (!cond_resched())
+					usleep_range(950, 1050);
+				return 0;
+			}
+		}
 
 		if (!cond_resched())
 			usleep_range(950, 1050);
diff --git a/include/drm/bridge/samsung-dsim.h b/include/drm/bridge/samsung-dsim.h
index 05100e91ecb9..6fc9bb2979e4 100644
--- a/include/drm/bridge/samsung-dsim.h
+++ b/include/drm/bridge/samsung-dsim.h
@@ -53,6 +53,7 @@ struct samsung_dsim_driver_data {
 	unsigned int plltmr_reg;
 	unsigned int has_freqband:1;
 	unsigned int has_clklane_stop:1;
+	unsigned int has_broken_fifoctrl_emptyhdr:1;
 	unsigned int num_clks;
 	unsigned int min_freq;
 	unsigned int max_freq;
-- 
2.34.1