[PATCH v2] drm: bridge: samsung-dsim: Fix waiting for empty cmd transfer FIFO on older Exynos

[Marek Szyprowski]

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.szyprow...@samsung.com>
Reviewed-by: Marek Vasut <ma...@denx.de>
---
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.szyprow...@samsung.com/
---
 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 9b7a00bafeaa..d06401de637c 100644
--- a/drivers/gpu/drm/bridge/samsung-dsim.c
+++ b/drivers/gpu/drm/bridge/samsung-dsim.c
@@ -412,6 +412,7 @@ 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 = {
@@ -428,6 +429,7 @@ 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 = {
@@ -1009,8 +1011,20 @@ 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..18017b3e5d9e 100644
--- a/include/drm/bridge/samsung-dsim.h
+++ b/include/drm/bridge/samsung-dsim.h
@@ -62,6 +62,7 @@ struct samsung_dsim_driver_data {
        const unsigned int *reg_values;
        u16 m_min;
        u16 m_max;
+       unsigned int has_broken_fifoctrl_emptyhdr;
 };
 
 struct samsung_dsim_host_ops {
-- 
2.34.1