From: Lee Jones <lee.jones@linaro.org>
To: Johan Hovold <johan@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, Johan Hovold <jhovold@gmail.com>
Subject: Re: [PATCH 2/5] mfd: lm3533-ctrlbank: Cap BRIGHTNESS_MAX to 127 since API uses u8 as carrier
Date: Mon, 29 Jun 2020 14:25:06 +0100 [thread overview]
Message-ID: <20200629132506.GJ177734@dell> (raw)
In-Reply-To: <20200629125102.GT3334@localhost>
On Mon, 29 Jun 2020, Johan Hovold wrote:
> On Mon, Jun 29, 2020 at 01:32:12PM +0100, Lee Jones wrote:
> > Since its conception in 2012 brightness has been artificially capped
> > at 127 since the variable carrying the value is u8. We could go to
> > the trouble of changing the whole API (crossing 3 different subsystems),
> > but clearly this hasn't bothered anyone in the best part of a decade.
> >
> > Simply, cap BRIGHTNESS_MAX to 127 instead (for now at least).
>
> Hmm. This patch is clearly broken and would contrary to the claim be
> introducing an artificial cap at half brightness. u8 can hold the max
> brightness value 255 just fine.
Yes, of course it can. Senior moment on my account.
> > Fixes the following W=1 warning(s):
> >
> > drivers/mfd/lm3533-ctrlbank.c: In function ‘lm3533_ctrlbank_set_brightness’:
> > drivers/mfd/lm3533-ctrlbank.c:98:10: warning: comparison is always false due to limited range of data type [-Wtype-limits]
> > 98 | if (val > LM3533_##_NAME##_MAX) | ^
> > drivers/mfd/lm3533-ctrlbank.c:125:1: note: in expansion of macro ‘lm3533_ctrlbank_set’
> > 125 | lm3533_ctrlbank_set(brightness, BRIGHTNESS);
> > | ^~~~~~~~~~~~~~~~~~~
>
> This warning is benign. The same macro is used to defined two function
> where in one case the max value coincides with U8_MAX so that the sanity
> check becomes redundant.
A benign warning, as most W=1 warnings are, is still a warning.
So how do you propose we fix it?
Is 255 a valid and used brightness level?
If so, how do you feel about:
/* Avoid 'always false' check '(u8) > 255' */
if (LM3533_##_NAME##_MAX != 0xff && val > LM3533_##_NAME##_MAX)
return -EINVAL;
> > Cc: Johan Hovold <jhovold@gmail.com>
> > Signed-off-by: Lee Jones <lee.jones@linaro.org>
> > ---
> > drivers/mfd/lm3533-ctrlbank.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/mfd/lm3533-ctrlbank.c b/drivers/mfd/lm3533-ctrlbank.c
> > index 34fba06ec7057..348ce67453092 100644
> > --- a/drivers/mfd/lm3533-ctrlbank.c
> > +++ b/drivers/mfd/lm3533-ctrlbank.c
> > @@ -17,7 +17,7 @@
> > #define LM3533_MAX_CURRENT_MAX 29800
> > #define LM3533_MAX_CURRENT_STEP 800
> >
> > -#define LM3533_BRIGHTNESS_MAX 255
> > +#define LM3533_BRIGHTNESS_MAX 127 /* Capped by API - could be up to 255 */
> > #define LM3533_PWM_MAX 0x3f
> >
> > #define LM3533_REG_PWM_BASE 0x14
>
> Johan
--
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
Follow Linaro: Facebook | Twitter | Blog
next prev parent reply other threads:[~2020-06-29 19:24 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-29 12:32 [PATCH 0/5] Last batch of W=1 warning fixes in MFD Lee Jones
2020-06-29 12:32 ` [PATCH 1/5] mfd: si476x-cmd: Add missing documentation for si476x_cmd_fm_rds_status()'s arg 'report' Lee Jones
2020-06-29 12:32 ` [PATCH 2/5] mfd: lm3533-ctrlbank: Cap BRIGHTNESS_MAX to 127 since API uses u8 as carrier Lee Jones
2020-06-29 12:51 ` Johan Hovold
2020-06-29 13:25 ` Lee Jones [this message]
2020-06-30 8:38 ` Johan Hovold
2020-06-29 12:32 ` [PATCH 3/5] mfd: rave-sp: Fix mistake in 'struct rave_sp_deframer's kerneldoc Lee Jones
2020-06-29 12:32 ` [PATCH 4/5] mfd: sprd-sc27xx-spi: Fix divide by zero when allocating register offset/mask Lee Jones
2020-06-29 13:06 ` Johan Hovold
2020-06-29 14:01 ` Lee Jones
2020-06-29 14:35 ` Baolin Wang
2020-06-29 14:43 ` Johan Hovold
2020-06-29 15:08 ` Baolin Wang
2020-06-29 15:45 ` Lee Jones
2020-07-01 9:15 ` [PATCH] mfd: sprd-sc27xx-spi: Fix-up bogus IRQ register offset and mask setting Lee Jones
2020-07-01 14:10 ` Baolin Wang
2020-06-29 12:32 ` [PATCH 5/5] mfd: axp20x-i2c: Do not define 'struct acpi_device_id' when !CONFIG_ACPI Lee Jones
2020-06-29 15:38 ` Chen-Yu Tsai
2020-07-06 7:31 ` Lee Jones
2020-07-01 6:59 ` [PATCH v2] mfd: axp20x-i2c: Tell the compiler that ACPI functions may not be used Lee Jones
2020-07-01 8:38 ` Chen-Yu Tsai
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