[PATCH] clk: samsung: exynos5433: use clock_ignore_unused flag for SPI3 related clocks

From: Jaehoon Chung <jh80.chung@samsung.com>

The SPI 3 bus uses two clocks, a bus clock and an input clock.
Do not disable the clocks when unused in order to allow access to
the SPI 3 device.

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Andi Shyti <redacted>
---
 drivers/clk/samsung/clk-exynos5433.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/clk/samsung/clk-exynos5433.c b/drivers/clk/samsung/clk-exynos5433.c
index 128527b..7c1fa09 100644
--- a/drivers/clk/samsung/clk-exynos5433.c
+++ b/drivers/clk/samsung/clk-exynos5433.c

@@ -1641,11 +1641,12 @@ static struct samsung_gate_clock peric_gate_clks[] __initdata = {
 	GATE(CLK_SCLK_IOCLK_SPI4, "sclk_ioclk_spi4", "ioclk_spi4_clk_in",
 			ENABLE_SCLK_PERIC, 21, CLK_SET_RATE_PARENT, 0),
 	GATE(CLK_SCLK_IOCLK_SPI3, "sclk_ioclk_spi3", "ioclk_spi3_clk_in",
-			ENABLE_SCLK_PERIC, 20, CLK_SET_RATE_PARENT, 0),
+			ENABLE_SCLK_PERIC, 20,
+			CLK_IGNORE_UNUSED | CLK_SET_RATE_PARENT, 0),
 	GATE(CLK_SCLK_SPI4, "sclk_spi4", "sclk_spi4_peric", ENABLE_SCLK_PERIC,
 			19, CLK_SET_RATE_PARENT, 0),
 	GATE(CLK_SCLK_SPI3, "sclk_spi3", "sclk_spi3_peric", ENABLE_SCLK_PERIC,
-			18, CLK_SET_RATE_PARENT, 0),
+			18, CLK_IGNORE_UNUSED | CLK_SET_RATE_PARENT, 0),
 	GATE(CLK_SCLK_SCI, "sclk_sci", "div_sclk_sci", ENABLE_SCLK_PERIC,
 			17, 0, 0),
 	GATE(CLK_SCLK_SC_IN, "sclk_sc_in", "div_sclk_sc_in", ENABLE_SCLK_PERIC,

-- 
2.8.1

Hi Andi, Jaehoon,

2016-06-17 17:16 GMT+09:00 Andi Shyti [off-list ref]:

From: Jaehoon Chung <jh80.chung@samsung.com>

The SPI 3 bus uses two clocks, a bus clock and an input clock.
Do not disable the clocks when unused in order to allow access to
the SPI 3 device.

If unused, why would access to SPI 3 device needed?

Best regards,
Tomasz

Hi Tomasz,

quoted

The SPI 3 bus uses two clocks, a bus clock and an input clock.
Do not disable the clocks when unused in order to allow access to
the SPI 3 device.

If unused, why would access to SPI 3 device needed?

because next I will submit a small driver which uses the SPI3.
Actually in the exynos5433 boards all the SPI are used but not all
the drivers are ported to mainline.

Thanks,
Andi

2016-06-19 14:59 GMT+09:00 Andi Shyti [off-list ref]:

Hi Tomasz,

quoted

quoted

The SPI 3 bus uses two clocks, a bus clock and an input clock.
Do not disable the clocks when unused in order to allow access to
the SPI 3 device.

If unused, why would access to SPI 3 device needed?

because next I will submit a small driver which uses the SPI3.
Actually in the exynos5433 boards all the SPI are used but not all
the drivers are ported to mainline.

Then shouldn't the driver request the clocks and enable them? Or I'm
missing something obvious? :)

Best regards,
Tomasz

Hi Tomasz,

quoted

quoted

quoted

The SPI 3 bus uses two clocks, a bus clock and an input clock.
Do not disable the clocks when unused in order to allow access to
the SPI 3 device.

If unused, why would access to SPI 3 device needed?

because next I will submit a small driver which uses the SPI3.
Actually in the exynos5433 boards all the SPI are used but not all
the drivers are ported to mainline.

Then shouldn't the driver request the clocks and enable them? Or I'm
missing something obvious? :)

the reason is that...

[ from the patch ]

        GATE(CLK_SCLK_IOCLK_SPI3, "sclk_ioclk_spi3", "ioclk_spi3_clk_in",
-                       ENABLE_SCLK_PERIC, 20, CLK_SET_RATE_PARENT, 0),
+                       ENABLE_SCLK_PERIC, 20,
+                       CLK_IGNORE_UNUSED | CLK_SET_RATE_PARENT, 0),

... the sclk_ioclk_spi3 is new in exynos5433 and there is no
implementation for enabling/disabling that particular clock...

        GATE(CLK_SCLK_SPI3, "sclk_spi3", "sclk_spi3_peric", ENABLE_SCLK_PERIC,
-                       18, CLK_SET_RATE_PARENT, 0),
+                       18, CLK_IGNORE_UNUSED | CLK_SET_RATE_PARENT, 0),

... while in this case your question makes sense, but it depends
on which clock the device (s3c64xx) is requesting (from the DTS).
In any case, I kept it consistent with the SPI1, which falls in
the same case, as in mainline we don't have any DTS for
exynos5433 (yet!).

Thanks,
Andi

2016-06-20 14:41 GMT+09:00 Andi Shyti [off-list ref]:

Hi Tomasz,

quoted

quoted

quoted

quoted

The SPI 3 bus uses two clocks, a bus clock and an input clock.
Do not disable the clocks when unused in order to allow access to
the SPI 3 device.

If unused, why would access to SPI 3 device needed?

because next I will submit a small driver which uses the SPI3.
Actually in the exynos5433 boards all the SPI are used but not all
the drivers are ported to mainline.

Then shouldn't the driver request the clocks and enable them? Or I'm
missing something obvious? :)

the reason is that...

[ from the patch ]

quoted

        GATE(CLK_SCLK_IOCLK_SPI3, "sclk_ioclk_spi3", "ioclk_spi3_clk_in",
-                       ENABLE_SCLK_PERIC, 20, CLK_SET_RATE_PARENT, 0),
+                       ENABLE_SCLK_PERIC, 20,
+                       CLK_IGNORE_UNUSED | CLK_SET_RATE_PARENT, 0),

... the sclk_ioclk_spi3 is new in exynos5433 and there is no
implementation for enabling/disabling that particular clock...

I'm not convinced that it's a good reason to make boards on which SPI3
is unused not gate the clock by default, then. The correct solution
would be to make the SPI driver request this clock and enable it.

quoted

        GATE(CLK_SCLK_SPI3, "sclk_spi3", "sclk_spi3_peric", ENABLE_SCLK_PERIC,
-                       18, CLK_SET_RATE_PARENT, 0),
+                       18, CLK_IGNORE_UNUSED | CLK_SET_RATE_PARENT, 0),

... while in this case your question makes sense, but it depends
on which clock the device (s3c64xx) is requesting (from the DTS).
In any case, I kept it consistent with the SPI1, which falls in
the same case, as in mainline we don't have any DTS for
exynos5433 (yet!).

Same here.

In general CLK_IGNORE_UNUSED should be avoided, because the semantics
of CLK_IGNORE_UNUSED are really weak and protect only from
clk_disable_unused(). It doesn't cause the clock to be enabled if it
was disabled at boot-up and it doesn't cause its parents to be enabled
(not even stay enabled if they don't have CLK_IGNORE_UNUSED, but have
gating capability). The only reasonable use case for it that I can
think of now is a display controller that needs certain clocks to
remain running to keep showing something on the screen until the
proper driver is loaded and takes over.

Unfortunately I have to NAK this patch. Please add proper support for
them to the SPI driver.

Best regards,
Tomasz

Unfortunately I have to NAK this patch. Please add proper support for
them to the SPI driver.

I agree, this is quite a lazy solution.

But your comment is giving me more work than what I was willing
to have, also because in this driver the SPI1 is aslo using
CLK_IGNORE_UNUSED :)

Thanks for your review,
Andi