Am Dienstag, 7. Mai 2019, 22:57:42 CEST schrieb Douglas Anderson: > There's a bit of math in rockchip_mmc_get_phase() to calculate the > "fine delay". This math boils down to: > > PSECS_PER_SEC = 1000000000000. > ROCKCHIP_MMC_DELAY_ELEMENT_PSEC = 60 > card_clk * ROCKCHIP_MMC_DELAY_ELEMENT_PSEC * 360 * x / PSECS_PER_SEC > > ...but we do it in pieces to avoid overflowing 32-bits. Right now we > overdo it a little bit, though, and end up getting less accurate math > than we could. Right now we do: > > DIV_ROUND_CLOSEST((card_clk / 1000000) * > (ROCKCHIP_MMC_DELAY_ELEMENT_PSEC / 10) * > (360 / 10) * > delay_num, > PSECS_PER_SEC / 1000000 / 10 / 10) > > This is non-ideal because: > A) The pins on Rockchip SoCs are rated to go at most 150 MHz, so the > max card clock is 150 MHz. Even ignoring this the maximum SD card > clock (for SDR104) would be 208 MHz. This means you can decrease > your division by 100x and still not overflow: > hex(208000000 / 10000 * 6 * 36 * 0xff) == 0x44497200 > B) On many Rockchip SoCs we end up with a card clock that is actually > 148500000 because we parent off the 297 MHz PLL. That means the > math we're actually doing today is less than ideal. Specifically: > 148500000 / 1000000 = 148 > > Let's fix the math to be slightly more accurate. > > NOTE: no known problems are fixed by this. It was found simply by > code inspection. If you want to see the difference between the old > and the new on a 148.5 MHz clock, this python can help: > > old = [x for x in > (int(round(148 * 6 * 36 * x / 10000.)) for x in range(256)) > if x < 90] > new = [x for x in > (int(round(1485 * 6 * 36 * x / 100000.)) for x in range(256)) > if x < 90] > > The only differences are: > delay_num=17 54=>55 > delay_num=22 70=>71 > delay_num=27 86=>87 > > Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx> gave this a spin on multiple socs and all of them still detected a hs200- card, so I've applied that for 5.3 Thanks Heiko _______________________________________________ Linux-rockchip mailing list Linux-rockchip@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/linux-rockchip
