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

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 ("drm: bridge: samsung-dsim: Drain command transfer FIFO before transfer").

Fixes: 14806c641582 ("drm: bridge: samsung-dsim: Drain command transfer FIFO before transfer")
Signed-off-by: Marek Szyprowski <[e-mail]>
Reviewed-by: Marek Vasut <[e-mail]>
Signed-off-by: Robert Foss <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/bridge/samsung-dsim.c

···
 	.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 = {
···
 	.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 = {
···
 	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);

include/drm/bridge/samsung-dsim.h

···
 	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;