On Wed, Dec 04, 2024 at 03:19:28PM +0000, Emil Renner Berthing wrote: > bigunclemax@ wrote: > > From: Maksim Kiselev <bigunclemax@xxxxxxxxx> > > > > In accordance with LicheePi 4A BSP the clock that comes to emmc/sdhci > > is 198Mhz. > > > > But changing from fixed-clock to CLK_EMMC_SDIO leads to increasing input > > clock from 198Mhz to 792Mhz. Because the CLK_EMMC_SDIO is actually 792Mhz. > > > > Therefore calculation of output SDCLK is incorrect now. > > The mmc driver sets the divisor to 4 times larger than it should be > > and emmc/sd works 4 times slower. > > > > This can be confirmed with fio test: > > Sequential read of emmc with fixed 198Mz clock: > > READ: bw=289MiB/s (303MB/s) > > > > Sequential read with CLK_EMMC_SDIO clock: > > READ: bw=82.6MiB/s (86.6MB/s) > > > > Let's fix this issue by providing fixed-factor-clock that divides > > CLK_EMMC_SDIO by 4 for emmc/sd nodes. > > Thanks for finding this bug! > > However, this feels like a work-around for a bug in the clock driver, and even > if there is a fixed factor divider somewhere this should probably be modelled > by the clock driver. Did you look into the documentation[1] and try to figure > out where eMMC clock comes from and where the /4 is missing? > > There is also a vendor tree somewhere with a much more complete clock driver. > Drew do you remember where it is? Maybe it's worth looking at how that driver > models the eMMC clocks. Sorry for the delay, I'm travelling until tomorrow. Maksim, thanks for finding this issue and sending a patch. That is a good point about checking the thead vendor kernel. I normally look at revy's thead-kernel repo [1] which is 5.10. revy also has a 6.6 lts branch in th1520-linux-kernel [2]. https://github.com/revyos/thead-kernel/tree/lpi4a/drivers/clk/thead Looking at line 454 in drivers/clk/thead/clk-light-fm.c [3]: clks[EMMC_SDIO_REF_CLK] = thead_light_clk_fixed_factor("emmc_sdio_ref_clk", "video_pll_foutpostdiv", 1, 4) /* Note: base clk is div 4 to 198M*/ Which derives from line 373: clks[VIDEO_PLL_FOUTPOSTDIV] = thead_clk_fixed("video_pll_foutpostdiv", 792000000); Thanks, Drew [1] https://github.com/revyos/thead-kernel [2] https://github.com/revyos/th1520-linux-kernel [3] https://github.com/revyos/thead-kernel/blob/lpi4a/drivers/clk/thead/clk-light-fm.c
