OMAP: DSS2: DISPC: Fix minimum PCD value

The current driver had a hardcoded minimum value of 2 for pixel clock
divisor (PCD). This doesn't seem to be right.

OMAP4 TRM says that PCD can be 1 when not downscaling, and inverted
pixel clock (IPC) is off.

OMAP3 TRM says the same, but also in the register descriptions that PCD
value 1 is invalid.

OMAP2 TRM says PCD 2 is the minimum.

OMAP2 is still untested, but for both OMAP3 and OMAP4 PCD of 1 seems to
work fine.

This patch adds a new DSS feature, FEAT_PARAM_DSS_PCD, which is used to
find the minimum and maximum PCD. The minimum is set to 2 for OMAP2, and
1 for OMAP3/4.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/video/omap2/dss/dispc.c

@@ -2334,7 +2334,7 @@ static void dispc_mgr_set_lcd_divisor(enum omap_channel channel, u16 lck_div,
 		u16 pck_div)
 {
 	BUG_ON(lck_div < 1);
-	BUG_ON(pck_div < 2);
+	BUG_ON(pck_div < 1);
 
 	dispc_write_reg(DISPC_DIVISORo(channel),
 			FLD_VAL(lck_div, 23, 16) | FLD_VAL(pck_div, 7, 0));
@@ -2721,19 +2721,25 @@ void dispc_mgr_set_pol_freq(enum omap_channel channel,
 void dispc_find_clk_divs(bool is_tft, unsigned long req_pck, unsigned long fck,
 		struct dispc_clock_info *cinfo)
 {
-	u16 pcd_min = is_tft ? 2 : 3;
+	u16 pcd_min, pcd_max;
 	unsigned long best_pck;
 	u16 best_ld, cur_ld;
 	u16 best_pd, cur_pd;
 
+	pcd_min = dss_feat_get_param_min(FEAT_PARAM_DSS_PCD);
+	pcd_max = dss_feat_get_param_max(FEAT_PARAM_DSS_PCD);
+
+	if (!is_tft)
+		pcd_min = 3;
+
 	best_pck = 0;
 	best_ld = 0;
 	best_pd = 0;
 
 	for (cur_ld = 1; cur_ld <= 255; ++cur_ld) {
 		unsigned long lck = fck / cur_ld;
 
-		for (cur_pd = pcd_min; cur_pd <= 255; ++cur_pd) {
+		for (cur_pd = pcd_min; cur_pd <= pcd_max; ++cur_pd) {
 			unsigned long pck = lck / cur_pd;
 			long old_delta = abs(best_pck - req_pck);
 			long new_delta = abs(pck - req_pck);
@@ -2768,7 +2774,7 @@ int dispc_calc_clock_rates(unsigned long dispc_fclk_rate,
 {
 	if (cinfo->lck_div > 255 || cinfo->lck_div == 0)
 		return -EINVAL;
-	if (cinfo->pck_div < 2 || cinfo->pck_div > 255)
+	if (cinfo->pck_div < 1 || cinfo->pck_div > 255)
 		return -EINVAL;
 
 	cinfo->lck = dispc_fclk_rate / cinfo->lck_div;

drivers/video/omap2/dss/dss_features.c

@@ -281,6 +281,7 @@ static const char * const omap4_dss_clk_source_names[] = {
 
 static const struct dss_param_range omap2_dss_param_range[] = {
 	[FEAT_PARAM_DSS_FCK]			= { 0, 173000000 },
+	[FEAT_PARAM_DSS_PCD]			= { 2, 255 },
 	[FEAT_PARAM_DSIPLL_REGN]		= { 0, 0 },
 	[FEAT_PARAM_DSIPLL_REGM]		= { 0, 0 },
 	[FEAT_PARAM_DSIPLL_REGM_DISPC]		= { 0, 0 },
@@ -291,6 +292,7 @@ static const struct dss_param_range omap2_dss_param_range[] = {
 
 static const struct dss_param_range omap3_dss_param_range[] = {
 	[FEAT_PARAM_DSS_FCK]			= { 0, 173000000 },
+	[FEAT_PARAM_DSS_PCD]			= { 1, 255 },
 	[FEAT_PARAM_DSIPLL_REGN]		= { 0, (1 << 7) - 1 },
 	[FEAT_PARAM_DSIPLL_REGM]		= { 0, (1 << 11) - 1 },
 	[FEAT_PARAM_DSIPLL_REGM_DISPC]		= { 0, (1 << 4) - 1 },
@@ -301,6 +303,7 @@ static const struct dss_param_range omap3_dss_param_range[] = {
 
 static const struct dss_param_range omap4_dss_param_range[] = {
 	[FEAT_PARAM_DSS_FCK]			= { 0, 186000000 },
+	[FEAT_PARAM_DSS_PCD]			= { 1, 255 },
 	[FEAT_PARAM_DSIPLL_REGN]		= { 0, (1 << 8) - 1 },
 	[FEAT_PARAM_DSIPLL_REGM]		= { 0, (1 << 12) - 1 },
 	[FEAT_PARAM_DSIPLL_REGM_DISPC]		= { 0, (1 << 5) - 1 },

drivers/video/omap2/dss/dss_features.h

@@ -77,6 +77,7 @@ enum dss_feat_reg_field {
 
 enum dss_range_param {
 	FEAT_PARAM_DSS_FCK,
+	FEAT_PARAM_DSS_PCD,
 	FEAT_PARAM_DSIPLL_REGN,
 	FEAT_PARAM_DSIPLL_REGM,
 	FEAT_PARAM_DSIPLL_REGM_DISPC,