soc: imx: gpc: Disable 6sl display power gating for ERR006287

The imx6sl chip errata document describes ERR006287 like this:

> Upon resuming from power gating, the modules in the display power domain
(eLCDIF, EPDC, PXP and SPDC) might fail to perform register reads
correctly.

> When the modules listed above are used, do not use power gating on the
display power domain.

Link: https://www.nxp.com/docs/en/errata/IMX6SLCE.pdf#page=62

Handle this in the safest possible way by keeping the DISP domain
always-on.

Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

drivers/soc/imx/gpc.c

@@ -288,26 +288,31 @@ static struct imx_pm_domain imx_gpc_domains[] = {
 struct imx_gpc_dt_data {
 	int num_domains;
 	bool err009619_present;
+	bool err006287_present;
 };
 
 static const struct imx_gpc_dt_data imx6q_dt_data = {
 	.num_domains = 2,
 	.err009619_present = false,
+	.err006287_present = false,
 };
 
 static const struct imx_gpc_dt_data imx6qp_dt_data = {
 	.num_domains = 2,
 	.err009619_present = true,
+	.err006287_present = false,
 };
 
 static const struct imx_gpc_dt_data imx6sl_dt_data = {
 	.num_domains = 3,
 	.err009619_present = false,
+	.err006287_present = true,
 };
 
 static const struct imx_gpc_dt_data imx6sx_dt_data = {
 	.num_domains = 4,
 	.err009619_present = false,
+	.err006287_present = false,
 };
 
 static const struct of_device_id imx_gpc_dt_ids[] = {
@@ -416,6 +421,11 @@ static int imx_gpc_probe(struct platform_device *pdev)
 		imx_gpc_domains[GPC_PGC_DOMAIN_PU].flags |=
 				PGC_DOMAIN_FLAG_NO_PD;
 
+	/* Keep DISP always on if ERR006287 is present */
+	if (of_id_data->err006287_present)
+		imx_gpc_domains[GPC_PGC_DOMAIN_DISPLAY].base.flags |=
+				GENPD_FLAG_ALWAYS_ON;
+
 	if (!pgc_node) {
 		ret = imx_gpc_old_dt_init(&pdev->dev, regmap,
 					  of_id_data->num_domains);