Re: [PATCH v3 29/65] clk: socfpga: gate: Add a determine_rate hook

Dinh Nguyen
2023-05-09T17:38:41Z

Hi Maxime,

On 5/4/23 12:04, Maxime Ripard wrote:
> Hi Dinh,
>
> On Thu, Apr 27, 2023 at 02:09:48PM -0500, Dinh Nguyen wrote:
>> Hi Maxime,
>>
>> On 4/25/23 09:48, Maxime Ripard wrote:
>>> Hi Dinh,
>>>
>>> On Mon, Apr 24, 2023 at 01:32:28PM -0500, Dinh Nguyen wrote:
>>>> On 4/4/23 05:11, Maxime Ripard wrote:
>>>>> The SoCFGPA gate clock implements a mux with a set_parent hook, but
>>>>> doesn't provide a determine_rate implementation.
>>>>>
>>>>> This is a bit odd, since set_parent() is there to, as its name implies,
>>>>> change the parent of a clock. However, the most likely candidate to
>>>>> trigger that parent change is a call to clk_set_rate(), with
>>>>> determine_rate() figuring out which parent is the best suited for a
>>>>> given rate.
>>>>>
>>>>> The other trigger would be a call to clk_set_parent(), but it's far less
>>>>> used, and it doesn't look like there's any obvious user for that clock.
>>>>>
>>>>> So, the set_parent hook is effectively unused, possibly because of an
>>>>> oversight. However, it could also be an explicit decision by the
>>>>> original author to avoid any reparenting but through an explicit call to
>>>>> clk_set_parent().
>>>>>
>>>>> The latter case would be equivalent to setting the flag
>>>>> CLK_SET_RATE_NO_REPARENT, together with setting our determine_rate hook
>>>>> to __clk_mux_determine_rate(). Indeed, if no determine_rate
>>>>> implementation is provided, clk_round_rate() (through
>>>>> clk_core_round_rate_nolock()) will call itself on the parent if
>>>>> CLK_SET_RATE_PARENT is set, and will not change the clock rate
>>>>> otherwise. __clk_mux_determine_rate() has the exact same behavior when
>>>>> CLK_SET_RATE_NO_REPARENT is set.
>>>>>
>>>>> And if it was an oversight, then we are at least explicit about our
>>>>> behavior now and it can be further refined down the line.
>>>>>
>>>>> Signed-off-by: Maxime Ripard <maxime@cerno.tech>
>>>>> ---
>>>>> drivers/clk/socfpga/clk-gate.c | 3 ++-
>>>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/clk/socfpga/clk-gate.c b/drivers/clk/socfpga/clk-gate.c
>>>>> index 32ccda960f28..cbba8462a09e 100644
>>>>> --- a/drivers/clk/socfpga/clk-gate.c
>>>>> +++ b/drivers/clk/socfpga/clk-gate.c
>>>>> @@ -110,6 +110,7 @@ static unsigned long socfpga_clk_recalc_rate(struct clk_hw *hwclk,
>>>>> static struct clk_ops gateclk_ops = {
>>>>> .recalc_rate = socfpga_clk_recalc_rate,
>>>>> + .determine_rate = __clk_mux_determine_rate,
>>>>> .get_parent = socfpga_clk_get_parent,
>>>>> .set_parent = socfpga_clk_set_parent,
>>>>> };
>>>>> @@ -166,7 +167,7 @@ void __init socfpga_gate_init(struct device_node *node)
>>>>> init.name = clk_name;
>>>>> init.ops = ops;
>>>>> - init.flags = 0;
>>>>> + init.flags = CLK_SET_RATE_NO_REPARENT;
>>>>> init.num_parents = of_clk_parent_fill(node, parent_name, SOCFPGA_MAX_PARENTS);
>>>>> if (init.num_parents < 2) {
>>>>>
>>>>
>>>> This patch broke SoCFPGA boot serial port. The characters are mangled.
>>>
>>> Do you have any other access to that board? If so, could you dump
>>> clk_summary in debugfs with and without that patch?
>>>
>>
>> That dump from the clk_summary are identical for both cases.
>
> Thanks for testing
>
> I'm a bit confused, there should be no difference in behaviour, and if
> there was any difference I would expect the clock tree to be somewhat
> different.
>
> Could you still paste the clk_summary (and dmesg) output? Which UART
> driver is being used?
>
> Also, is there a way for me to test it somehow?
>

Apologies, but there is a diff with/without this patch:

With patch:
< l4_sp_clk 3 3 0 100000000
0 0 50000 ?
---
Without patch:
> l4_sp_clk 4 4 0 100000000
0 0 50000 ?

The enable/prepare count is 4 instead of 3 in the case of a working
UART. The debug uart is using the lp_sp_clk.

The Cyclone5 devkits are pretty cheap if you want to get one.

Here is the full out of clk_summary:

# cat /sys/kernel/debug/clk/clk_summary
enable prepare protect
duty hardware
clock count count count rate
accuracy phase cycle enable
-------------------------------------------------------------------------------------------------------
osc1 5 5 0 25000000
0 0 50000 Y
sdram_pll 0 0 0 800000000
0 0 50000 Y
h2f_usr2_clk 0 0 0 133333333
0 0 50000 Y
h2f_user2_clk 0 0 0 133333333
0 0 50000 ?
ddr_dq_clk 0 0 0 400000000
0 0 50000 Y
ddr_dq_clk_gate 0 0 0 400000000
0 0 50000 ?
ddr_2x_dqs_clk 0 0 0 800000000
0 0 50000 Y
ddr_2x_dqs_clk_gate 0 0 0 800000000
0 0 50000 ?
ddr_dqs_clk 0 0 0 400000000
0 0 50000 Y
ddr_dqs_clk_gate 0 0 0 400000000
0 0 50000 ?
periph_pll 3 3 0 1000000000
0 0 50000 Y
h2f_usr1_clk 0 0 0 1953125
0 0 50000 Y
h2f_user1_clk 0 0 0 1953125
0 0 50000 ?
per_base_clk 4 4 0 200000000
0 0 50000 Y
gpio_db_clk 0 0 0 32000
0 0 50000 ?
can1_clk 0 0 0 40000000
0 0 50000 ?
can0_clk 0 0 0 100000000
0 0 50000 ?
spi_m_clk 1 1 0 200000000
0 0 50000 ?
usb_mp_clk 1 1 0 200000000
0 0 50000 ?
l4_sp_clk 4 4 0 100000000
0 0 50000 ?
l4_mp_clk 1 1 0 100000000
0 0 50000 ?
per_nand_mmc_clk 1 1 0 200000000
0 0 50000 Y
nand_x_clk 0 0 0 200000000
0 0 50000 ?
nand_clk 0 0 0 50000000
0 0 50000 ?
nand_ecc_clk 0 0 0 200000000
0 0 50000 ?
sdmmc_clk 1 1 0 200000000
0 0 50000 ?
sdmmc_clk_divided 1 1 0 50000000
0 0 50000 ?
per_qsi_clk 0 0 0 1953125
0 0 50000 Y
emac1_clk 1 1 0 250000000
0 0 50000 Y
emac_1_clk 1 1 0 250000000
0 0 50000 ?
emac0_clk 0 0 0 1953125
0 0 50000 Y
emac_0_clk 0 0 0 1953125
0 0 50000 ?
dbg_base_clk 0 0 0 6250000
0 0 50000 Y
dbg_timer_clk 0 0 0 6250000
0 0 50000 ?
dbg_trace_clk 0 0 0 6250000
0 0 50000 ?
dbg_at_clk 0 0 0 6250000
0 0 50000 ?
dbg_clk 0 0 0 3125000
0 0 50000 ?
main_pll 2 3 0 1850000000
0 0 50000 Y
cfg_h2f_usr0_clk 0 0 0 123333333
0 0 50000 Y
h2f_user0_clk 0 0 0 123333333
0 0 50000 ?
cfg_clk 0 0 0 123333333
0 0 50000 ?
main_nand_sdmmc_clk 0 0 0 3613281
0 0 50000 Y
main_qspi_clk 1 1 0 370000000
0 0 50000 Y
qspi_clk 1 1 0 370000000
0 0 50000 ?
mainclk 0 1 0 370000000
0 0 50000 Y
l3_mp_clk 0 0 0 185000000
0 0 50000 ?
l3_sp_clk 0 0 0 92500000
0 0 50000 Y
l3_main_clk 0 0 0 370000000
0 0 50000 Y
l4_main_clk 0 1 0 370000000
0 0 50000 ?
mpuclk 1 1 0 925000000
0 0 50000 Y
mpu_l2_ram_clk 0 0 0 462500000
0 0 50000 Y
mpu_periph_clk 1 1 0 231250000
0 0 50000 Y

Dinh