Re: [PATCH v3 03/15] soc: tegra: Add Tegra PMC clock registrations into PMC driver

From: Sowjanya Komatineni
Date: Wed Dec 11 2019 - 13:50:25 EST


On 12/10/19 5:06 PM, Sowjanya Komatineni wrote:

On 12/10/19 9:41 AM, Dmitry Osipenko wrote:
10.12.2019 19:53, Sowjanya Komatineni ÐÐÑÐÑ:
On 12/9/19 3:03 PM, Sowjanya Komatineni wrote:
On 12/9/19 12:46 PM, Sowjanya Komatineni wrote:
On 12/9/19 12:12 PM, Dmitry Osipenko wrote:
08.12.2019 00:36, Sowjanya Komatineni ÐÐÑÐÑ:
On 12/7/19 11:59 AM, Sowjanya Komatineni wrote:
On 12/7/19 8:00 AM, Dmitry Osipenko wrote:
07.12.2019 18:53, Dmitry Osipenko ÐÐÑÐÑ:
07.12.2019 18:47, Dmitry Osipenko ÐÐÑÐÑ:
07.12.2019 17:28, Dmitry Osipenko ÐÐÑÐÑ:
06.12.2019 05:48, Sowjanya Komatineni ÐÐÑÐÑ:
Tegra210 and prior Tegra PMC has clk_out_1, clk_out_2, clk_out_3
with
mux and gate for each of these clocks.

Currently these PMC clocks are registered by Tegra clock driver
using
clk_register_mux and clk_register_gate by passing PMC base
address
and register offsets and PMC programming for these clocks
happens
through direct PMC access by the clock driver.

With this, when PMC is in secure mode any direct PMC access
from the
non-secure world does not go through and these clocks will
not be
functional.

This patch adds these clocks registration with PMC as a clock
provider
for these clocks. clk_ops callback implementations for these
clocks
uses tegra_pmc_readl and tegra_pmc_writel which supports PMC
programming
in secure mode and non-secure mode.

Signed-off-by: Sowjanya Komatineni <skomatineni@xxxxxxxxxx>
---
[snip]

+
+static const struct clk_ops pmc_clk_gate_ops = {
+ÂÂÂ .is_enabled = pmc_clk_is_enabled,
+ÂÂÂ .enable = pmc_clk_enable,
+ÂÂÂ .disable = pmc_clk_disable,
+};
What's the benefit of separating GATE from the MUX?

I think it could be a single clock.
According to TRM:

1. GATE and MUX are separate entities.

2. GATE is the parent of MUX (see PMC's CLK_OUT paths diagram
in TRM).

3. PMC doesn't gate EXTPERIPH clock but could "force-enable" it,
correct?
Was following existing clk-tegra-pmc as I am not sure of reason for
having these clocks registered as separate mux and gate clocks.

Yes, PMC clocks can be registered as single clock and can use clk_ops
for set/get parent and enable/disable.

enable/disable of PMC clocks is for force-enable to force the clock to
run regardless of ACCEPT_REQ or INVERT_REQ.

4. clk_m_div2/4 are internal PMC OSC dividers and thus these clocks
should belong to PMC.
Also, it should be "osc" and not "clk_m".
I followed the same parents as it were in existing clk-tegra-pmc
driver.

Yeah they are wrong and they should be from osc and not clk_m.

Will fix in next version.

Reg clk_m_div2/3, they are dividers at OSC pad and not really internal
to PMC block.

current clock driver creates clk_m_div clocks which should actually be
osc_div2/osc_div4 clocks with osc as parent.

There are no clk_m_div2 and clk_m_div4 from clk_m

Will fix this in next version.

Could you please describe the full EXTPERIPH clock topology and how the
pinmux configuration is related to it all?

What is internal to the Tegra chip and what are the external outputs?

Is it possible to bypass PMC on T30+ for the EXTPERIPH clocks?
PMC CLK1/2/3 possible sources are OSC_DIV1, OSC_DIV2, OSC_DIV4,
EXTPERIPH from CAR.

OSC_DIV1/2/4 are with internal dividers at the OSC Pads

EXTPERIPH is from CAR and it has reset and enable controls along with
clock source selections to choose one of the PLLA_OUT0, CLK_S,
PLLP_OUT0, CLK_M, PLLE_OUT0

So, PMC CLK1/2/4 possible parents are OSC_DIV1, OSC_DIV2, OSC_DIV4,
EXTERN.


CLK1/2/3 also has Pinmux to route EXTPERIPH output on to these pins.


When EXTERN output clock is selected for these PMC clocks thru
CLKx_SRC_SEL, output clock is from driver by EXTPERIPH from CAR via
Pinmux logic or driven as per CLKx_SRC_SEL bypassing pinmux based on
CLKx_ACCEPT_REQ bit.


PMC Clock control register has bit CLKx_ACCEPT_REQ
When CLKx_ACCEPT_REQ = 0, output clock driver is from by EXTPERIPH
through the pinmux
When CLKx_ACCEPT_REQ = 1, output clock is based on CLKx_SRC_SEL bits
(OSC_DIV1/2/4 and EXTPERIPH clock bypassing the pinmux)

FORCE_EN bit in PMC CLock control register forces the clock to run
regardless of this.
PMC clock gate is based on the state of CLKx_ACCEPT_REQ and FORCE_EN
like explained above.

CLKx_ACCEPT_REQ is 0 default and FORCE_EN acts as gate to enable/disable
EXTPERIPH clock output to PMC CLK_OUT_1/2/3.
[and to enable OSC as well]

So I believe we need to register as MUX and Gate rather than as a single
clock. Please confirm.
1. The force-enabling is applied to both OSC and EXTERN sources of
PMC_CLK_OUT_x by PMC at once.

2. Both of PMC's force-enabling and OSC/EXTERN selection is internal to PMC.

Should be better to define it as a single "pmc_clk_out_x". I don't see
any good reasons for differentiating PMC's Gate from the MUX, it's a
single hardware unit from a point of view of the rest of the system.

Peter, do you have any objections?

We added fallback option for audio mclk and also added check for assigned-clock-parents dt property in audio driver and if its not then we do parent init configuration in audio driver.

Current clock driver creates 2 separate clocks clk_out_1_mux and clk_out_1 for each pmc clock in clock driver and uses extern1 as parent to clk_out_1_mux and clk_out_1_mux is parent to clk_out_1.

With change of registering each pmc clock as a single clock, when we do parent init assignment in audio driver when assigned-clock-properties are not used in DT (as we removed parent inits for extern and clk_outs from clock driver), we should still try to get clock based on clk_out_1_mux as parent assignment of extern1 is for clk_out_1_mux as per existing clock tree.

clk_out_1_mux clock retrieve will fail with this change of single clock when any new platform device tree doesn't specify assigned-clock-parents properties and tegra_asoc_utils_init fails.

With single clock, extern1 is the parent for clk_out_1 and with separate clocks for mux and gate, extern1 is the parent for clk_out_1_mux.

If we move to single clock now, it need one more additional fallback implementation in audio driver during parent configuration as clk_out_1_mux will not be there with single clock change and old/current kernel has it as it uses separate clocks for pmc mux and gate.

Also, with single clock for both PMC mux and gate now, new DT should use extern1 as parent to CLK_OUT_1 as CLK_OUT_1_MUX will not be there old PMC dt-bindings has separate clocks for MUX (CLK_OUT_1_MUX) and gate (CLK_OUT_1)

DT bindings will not be compatible b/w old and new changes if we move to Single PMC clock now.

Should we go with same separate clocks to have it compatible to avoid all this?