1 files changed, 18 insertions, 6 deletions

diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
index aec97c8e5ac4..7a365df91c53 100644
--- a/drivers/gpu/drm/msm/dsi/dsi_host.c
+++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
@@ -33,17 +33,24 @@
 static int dsi_get_version(const void __iomem *base, u32 *major, u32 *minor)
 {
         u32 ver;
-        u32 ver_6g;
 
         if (!major || !minor)
                 return -EINVAL;
 
-        /* From DSI6G(v3), addition of a 6G_HW_VERSION register at offset 0
+        /*
+         * From DSI6G(v3), addition of a 6G_HW_VERSION register at offset 0
          * makes all other registers 4-byte shifted down.
+         *
+         * In order to identify between DSI6G(v3) and beyond, and DSIv2 and
+         * older, we read the DSI_VERSION register without any shift(offset
+         * 0x1f0). In the case of DSIv2, this hast to be a non-zero value. In
+         * the case of DSI6G, this has to be zero (the offset points to a
+         * scratch register which we never touch)
          */
-        ver_6g = msm_readl(base + REG_DSI_6G_HW_VERSION);
-        if (ver_6g == 0) {
-                ver = msm_readl(base + REG_DSI_VERSION);
+
+        ver = msm_readl(base + REG_DSI_VERSION);
+        if (ver) {
+                /* older dsi host, there is no register shift */
                 ver = FIELD(ver, DSI_VERSION_MAJOR);
                 if (ver <= MSM_DSI_VER_MAJOR_V2) {
                         /* old versions */
@@ -54,12 +61,17 @@ static int dsi_get_version(const void __iomem *base, u32 *major, u32 *minor)
                         return -EINVAL;
                 }
         } else {
+                /*
+                 * newer host, offset 0 has 6G_HW_VERSION, the rest of the
+                 * registers are shifted down, read DSI_VERSION again with
+                 * the shifted offset
+                 */
                 ver = msm_readl(base + DSI_6G_REG_SHIFT + REG_DSI_VERSION);
                 ver = FIELD(ver, DSI_VERSION_MAJOR);
                 if (ver == MSM_DSI_VER_MAJOR_6G) {
                         /* 6G version */
                         *major = ver;
-                        *minor = ver_6g;
+                        *minor = msm_readl(base + REG_DSI_6G_HW_VERSION);
                         return 0;
                 } else {
                         return -EINVAL;