# \[PATCH V3 2/2\] backlight: qcom-wled: Correct the sync\_toggle sequence - Subsystems: FRAMEBUFFER LAYER, ARM/QUALCOMM MAILING LIST, BACKLIGHT CLASS/SUBSYSTEM, THE REST - Maintainers: Helge Deller, Lee Jones, Daniel Thompson, Jingoo Han, Linus Torvalds - Status: SUPERSEDED (Superseded by v5 posted 2021-03-18) - Superseded by v5 (posted 2021-03-18). - Revision v3 (5 revisions archived). - List: linux-fbdev - 3 messages, 2 authors - Page: https://ratatoskr.run/linux-fbdev/2021/03/6281236/t ## \[PATCH V3 2/2\] backlight: qcom-wled: Correct the sync\_toggle sequence - From: Kiran Gunda \ - Date: 2021-03-01 09:30:30 - Message: https://ratatoskr.run/linux-fbdev/2021/03/6281236.md ```text As per the current implementation, after FSC (Full Scale Current) and brightness update the sync bits are transitioned from set-then-clear. But, the FSC and brightness sync takes place during a clear-then-set 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 --- 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 ``` ## Re: \[PATCH V3 2/2\] backlight: qcom-wled: Correct the sync\_toggle sequence - From: Daniel Thompson \ - Date: 2021-03-01 10:05:57 - Message: https://ratatoskr.run/linux-fbdev/2021/03/6281288.md ```text On Mon, Mar 01, 2021 at 02:58:36PM +0530, Kiran Gunda wrote: > As per the current implementation, after FSC (Full Scale Current) > and brightness update the sync bits are transitioned from set-then-clear. This does not makes sense since there are too many verbs. Set and clear are both verbs so in this context: "the code will set the bit and then the code will clear the bit". Either: s/transitioned from set-then-clear/set-then-cleared/. Or: s/transitioned from set-then-clear/using a set-then-clear approach/. > But, the FSC and brightness sync takes place during a clear-then-set > transition of the sync bits. Likewise this no longer makes sense and had also become misleading. Two changes of state, clear and then set, do not usually result in a single transition. Either: s/clear-then-set/0 to 1/ Alternatively, if you want to stick exclusively to the set/clear terminology then replace the whole quoted section with: But, the FSC and brightness sync takes place when the sync bits are set (e.g. on a rising edge). > 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 With one of each of the changes proposed above: Reviewed-by: Daniel Thompson Daniel. > --- > 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 > ``` ## Re: \[PATCH V3 2/2\] backlight: qcom-wled: Correct the sync\_toggle sequence - From: \ - Date: 2021-03-01 18:49:44 - Message: https://ratatoskr.run/linux-fbdev/2021/03/6282050.md ```text On 2021-03-01 15:32, Daniel Thompson wrote: > On Mon, Mar 01, 2021 at 02:58:36PM +0530, Kiran Gunda wrote: >> As per the current implementation, after FSC (Full Scale Current) >> and brightness update the sync bits are transitioned from set-then-clear. > > This does not makes sense since there are too many verbs. Set and clear > are both verbs so in this context: "the code will set the bit and then > the code will clear the bit". > > Either: > > s/transitioned from set-then-clear/set-then-cleared/. > > Or: > > s/transitioned from set-then-clear/using a set-then-clear approach/. > >> But, the FSC and brightness sync takes place during a clear-then-set >> transition of the sync bits. > > Likewise this no longer makes sense and had also become misleading. > Two changes of state, clear and then set, do not usually result in a > single transition. > > Either: > > s/clear-then-set/0 to 1/ > > Alternatively, if you want to stick exclusively to the set/clear > terminology then replace the whole quoted section with: > > But, the FSC and brightness sync takes place when the sync bits are > set (e.g. on a rising edge). > > >> 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 > > With one of each of the changes proposed above: > Reviewed-by: Daniel Thompson > > > Daniel. > Apologies for the mistake. I have corrected and submitted the V4 series with the "reviewed-by" tag. > >> --- >> 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 >> ```