[PATCH 2/2] soc/imx: add workaround for i.MX6QP to the GPC PD driver

Am Donnerstag, den 30.03.2017, 09:08 +0200 schrieb Lothar Wa?mann:

Hi,

On Wed, 29 Mar 2017 18:13:46 +0200 Lucas Stach wrote:

quoted

Am Mittwoch, den 29.03.2017, 16:08 +0000 schrieb A.S. Dong:

quoted

Hi Lucas,

quoted

-----Original Message-----
From: Lucas Stach [mailto:l.stach at pengutronix.de]
Sent: Thursday, March 23, 2017 10:44 PM
To: Shawn Guo
Cc: Fabio Estevam; A.S. Dong; devicetree at vger.kernel.org; linux-arm-
kernel at lists.infradead.org; kernel at pengutronix.de; patchwork-
lst at pengutronix.de
Subject: [PATCH 2/2] soc/imx: add workaround for i.MX6QP to the GPC PD
driver

On i.MX6QP, due to hardware erratum ERR009619, the PRE clocks may be
stalled during the power up sequencing of the PU power domain. As this may
lead to a complete loss of display output, the recommended workaround is
to keep the PU domain enabled during normal system operation.

Implement this by rejecting the domain power down request on the affected
SoC.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
---
 drivers/soc/imx/gpc.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/soc/imx/gpc.c b/drivers/soc/imx/gpc.c index

4294287e5f6c..599e1e46f694 100644

--- a/drivers/soc/imx/gpc.c
+++ b/drivers/soc/imx/gpc.c

@@ -45,6 +45,7 @@ struct imx_pm_domain {
 	unsigned int reg_offs;
 	signed char cntr_pdn_bit;
 	unsigned int ipg_rate_mhz;
+	bool allow_dynamic_pd;
 };

 static inline struct imx_pm_domain *

@@ -59,6 +60,9 @@ static int imx6_pm_domain_power_off(struct

generic_pm_domain *genpd)
 	int iso, iso2sw;
 	u32 val;

+	if (!pd->allow_dynamic_pd)
+		return -EBUSY;
+
 	/* Read ISO and ISO2SW power down delays */
 	regmap_read(pd->regmap, pd->reg_offs + GPC_PGC_PUPSCR_OFFS, &val);
 	iso = val & 0x3f;

@@ -255,6 +259,7 @@ static struct imx_pm_domain imx_gpc_domains[] = {
 		},
 		.reg_offs = 0x260,
 		.cntr_pdn_bit = 0,
+		.allow_dynamic_pd = true,
 	}, {
 		.base = {
 			.name = "DISPLAY",

@@ -263,23 +268,33 @@ static struct imx_pm_domain imx_gpc_domains[] = {
 		},
 		.reg_offs = 0x240,
 		.cntr_pdn_bit = 4,
+		.allow_dynamic_pd = true,

Just a Nitpick, besides shawn's comment in another mail,
if we use a domain flag like IMX_PD_ALWAYS_ON set by SoC errata flag,
then probably we can save all the default allow_dynamic_pd lines.
This also release the life when adding new domains.

If other things like that show up we can certainly switch to a flags
field. In the meantime I like that the current style is more explicit
about it.

Since the purpose of the driver is all about dynamic power management,
I would rather add a 'disable_dynamic_pd' for the case(s) where it's
not allowed, rather than having to state the obvious over and over
again.

Convincing argument. I'll change that in v2.

Regards,
Lucas