Quoting Mike Looijmans (2021-01-05 23:04:36) > Export an attribute program_nvm_bank that when read reports the current > bank value. To program the chip's current state into NVM, write the > magic value 0xC7 into this attribute. > > This allows the clock chip to be programmed "in system" to reduce boot > time by 300ms and allows the clock to be up and running before the > kernel boots (e.g. for bootloader usage). Some vendors initialize PLLs > only in their bootloader and thus need the clock running at boot. > > Signed-off-by: Mike Looijmans <[email protected]> > --- > v2: Add description in Documentation/ABI/ > Use regmap_read_poll_timeout() > Abort on sysfs_create_group error > > .../ABI/testing/sysfs-devices-clk-si5341 | 24 +++++++ > drivers/clk/clk-si5341.c | 68 +++++++++++++++++++ > 2 files changed, 92 insertions(+) > create mode 100644 Documentation/ABI/testing/sysfs-devices-clk-si5341 > > diff --git a/Documentation/ABI/testing/sysfs-devices-clk-si5341 > b/Documentation/ABI/testing/sysfs-devices-clk-si5341 > new file mode 100644 > index 000000000000..7243b82a3729 > --- /dev/null > +++ b/Documentation/ABI/testing/sysfs-devices-clk-si5341 > @@ -0,0 +1,24 @@ > +What: /sys/bus/i2c/devices/.../clk-si534*/program_nvm_bank
I'm still curious why this is exposed here instead of through nvmem framework. I think we talked about it before, but it would be great if the commit text could quiet any concerns about that so we have a record of why using the existing nvmem framework wasn't suitable. > +Date: Jan 2021 > +KernelVersion: 5.12 > +Contact: Mike Looijmans <[email protected]> > +Description: Allows programming the NVM memory of the clock chip, so it > boots > + up in the current configuration. This saves boot time (300ms > + clock initialization) and allows the clock to be available > + before the kernel boots (e.g. u-boot ethernet clock). > + > + Write the magic value 0xc7 to this attribute to program the > + chip's current settings into its NVM storage. This magic value > + is taken from the datasheet, it's the same value that must be > + written to the hardware to program it. Programming can only be > + done twice in the lifetime of the chip. > + > + Read the value to check the state of the chip. This returns > the > + raw value as read from the hardware. Possible values: > + 0x03: Not programmed > + 0x0f: Programmed once > + 0x3f: Programmed twice, can no longer be programmed > + > +Users: User space applications for embedded boards equipped with one > + or more Si534x programmable clock devices. Would typically be > + used at the end of production stages.
