On Mon, Sep 08, 2025 at 11:49:51AM +0200, Krzysztof Kozlowski wrote: > Hardware Programming Guide for DSI PHY says that PLL_SHUTDOWNB and > DIGTOP_PWRDN_B have to be asserted for any PLL register access. > Whenever dsi_pll_7nm_vco_recalc_rate() or dsi_pll_7nm_vco_set_rate() > were called on unprepared PLL, driver read values of zero leading to all > sort of further troubles, like failing to set pixel and byte clock > rates. > > Asserting the PLL shutdown bit is done by dsi_pll_enable_pll_bias() (and > corresponding dsi_pll_disable_pll_bias()) which are called through the > code, including from PLL .prepare() and .unprepare() callbacks. > > The .set_rate() and .recalc_rate() can be called almost anytime from > external users including times when PLL is or is not prepared, thus > driver should not interfere with the prepare status. > > Implement simple reference counting for the PLL bias, so > set_rate/recalc_rate will not change the status of prepared PLL. > > Issue of reading 0 in .recalc_rate() did not show up on existing > devices, but only after re-ordering the code for SM8750. > > Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlow...@linaro.org> > > --- > > Continuing changelog from "drm/msm: Add support for SM8750" where this > was part of. > > Changes in v7: > - Rebase > - I did not remove ndelay(250) as discussed with Dmitry, because: > 1. Indeed the HPG does not mention any delay needed, unlike PHY 10 nm. > 2. However downstream source code for PHY 3+4+5 nm has exactly these > delays. This could be copy-paste or could be intentional workaround > for some issue about which I have no clue. Timings are tricky and > I don't think I should be introducing changes without actually > knowing them. > - Add Rb tags > - Link to v6: > https://lore.kernel.org/r/20250610-b4-sm8750-display-v6-0-ee633e3dd...@linaro.org > > Changes in v6: > 1. Print error on pll bias enable/disable imbalance refcnt > > Changes in v5: > 1. New patch > --- > drivers/gpu/drm/msm/dsi/phy/dsi_phy.h | 1 + > drivers/gpu/drm/msm/dsi/phy/dsi_phy_7nm.c | 53 +++++++++++++++++++++++ > 2 files changed, 54 insertions(+) >
Reviewed-by: Dmitry Baryshkov <dmitry.barysh...@oss.qualcomm.com> -- With best wishes Dmitry
