Re: [PATCH V2 2/2] backlight: qcom-wled: Correct the sync_toggle sequence
From: Daniel Thompson <hidden>
Date: 2021-02-26 17:27:49
Also in:
dri-devel, linux-arm-msm, linux-fbdev, linux-leds, lkml, phone-devel
On Fri, Feb 26, 2021 at 05:42:24PM +0530, Kiran Gunda wrote:
As per the current implementation, after FSC (Full Scale Current) and brightness update the sync bits are transitioned from 1 to 0.
This still seems to incorrectly describe the current behaviour. Surely in most cases (i.e. every time except the first) the value of the sync bit is 0 when the function is called and we get both a 0 to 1 and then a 1 to 0 transition. That is why I recommended set-then-clear terminology to describe the current behaviour. It is concise and correct. Daniel.
quoted hunk ↗ jump to hunk
But, the FSC and brightness sync takes place during a 0 to 1 transition of the sync bits. So the hardware team recommends a clear-then-set approach in order to guarantee such a transition regardless of the previous register state. Signed-off-by: Kiran Gunda <redacted> --- drivers/video/backlight/qcom-wled.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c index aef52b9..19f83ac 100644 --- a/drivers/video/backlight/qcom-wled.c +++ b/drivers/video/backlight/qcom-wled.c@@ -337,13 +337,13 @@ static int wled3_sync_toggle(struct wled *wled) rc = regmap_update_bits(wled->regmap, wled->ctrl_addr + WLED3_SINK_REG_SYNC, - mask, mask); + mask, WLED3_SINK_REG_SYNC_CLEAR); if (rc < 0) return rc; rc = regmap_update_bits(wled->regmap, wled->ctrl_addr + WLED3_SINK_REG_SYNC, - mask, WLED3_SINK_REG_SYNC_CLEAR); + mask, mask); return rc; }@@ -353,17 +353,17 @@ static int wled5_mod_sync_toggle(struct wled *wled) int rc; u8 val; - val = (wled->cfg.mod_sel == MOD_A) ? WLED5_SINK_REG_SYNC_MOD_A_BIT : - WLED5_SINK_REG_SYNC_MOD_B_BIT; rc = regmap_update_bits(wled->regmap, wled->sink_addr + WLED5_SINK_REG_MOD_SYNC_BIT, - WLED5_SINK_REG_SYNC_MASK, val); + WLED5_SINK_REG_SYNC_MASK, 0); if (rc < 0) return rc; + val = (wled->cfg.mod_sel == MOD_A) ? WLED5_SINK_REG_SYNC_MOD_A_BIT : + WLED5_SINK_REG_SYNC_MOD_B_BIT; return regmap_update_bits(wled->regmap, wled->sink_addr + WLED5_SINK_REG_MOD_SYNC_BIT, - WLED5_SINK_REG_SYNC_MASK, 0); + WLED5_SINK_REG_SYNC_MASK, val); } static int wled_ovp_fault_status(struct wled *wled, bool *fault_set)-- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project