Re: [PATCH v2 2/3] clk: samsung: gs101: propagate PERIC1 USI SPI clock rate

[André Draszik]

On Tue, 2024-03-26 at 17:28 +0000, Tudor Ambarus wrote:
> When SPI transfer is being prepared, the spi-s3c64xx driver will call
> clk_set_rate() to change the rate of SPI source clock (IPCLK). But IPCLK
> is a gate (leaf) clock, so it must propagate the rate change up the
> clock tree, so that corresponding MUX/DIV clocks can actually change
> their values. Add CLK_SET_RATE_PARENT flag to corresponding clocks for
> all USI instances in GS101 PERIC1: USI{0, 9, 10, 11, 12, 13}. This change
> involves the following clocks:
> 
> PERIC1 USI*:
> 
>     Clock                              Div range    MUX Selection
>     -------------------------------------------------------------------
>     gout_peric1_peric1_top0_ipclk_*    -            -
>     dout_peric1_usi*_usi               /1..16       -
>     mout_peric1_usi*_usi_user          -            {24.5 MHz, 400 MHz}
> 
> With input clock of 400 MHz this scheme provides the following IPCLK
> rate range, for each USI block:
> 
>     PERIC1 USI*:       1.5 MHz ... 400 MHz
> 
> Accounting for internal /4 divider in SPI blocks, and because the max
> SPI frequency is limited at 50 MHz, it gives us next SPI SCK rates:
> 
>     PERIC1 USI_SPI*:   384 KHz ... 49.9 MHz
> 
> Which shall be fine for the applications of the SPI bus.
> 
> Note that with this we allow the reparenting of the MUX_USIx clocks to
> OSCCLK. Each instance of the USI IP has its own MUX_USI clock, thus the
> reparenting of a MUX_USI clock corresponds to a single instance of the
> USI IP. The datasheet mentions OSCCLK just in the low-power mode
> context, but the downstream driver reparents too the MUX_USI clocks to
> OSCCLK. Follow the downstream driver and do the same.
> 
> Fixes: 63b4bd1259d9 ("clk: samsung: gs101: add support for cmu_peric1")
> Signed-off-by: Tudor Ambarus <tudor.ambarus@xxxxxxxxxx>

Acked-by: André Draszik <andre.draszik@xxxxxxxxxx>