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From: Delphine_CC_Chiu/WYHQ/Wiwynn <Delphine_CC_Chiu@wiwynn.com>
To: Guenter Roeck <linux@roeck-us.net>, Delphine_CC_Chiu/WYHQ/Wiwynn
	<Delphine_CC_Chiu@wiwynn.com>
CC: "patrick@stwcx.xyz" <patrick@stwcx.xyz>, Jean Delvare <jdelvare@suse.com>,
	"linux-hwmon@vger.kernel.org" <linux-hwmon@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH v1] hwmon: max31790: revise the scale to write pwm
Thread-Topic: [PATCH v1] hwmon: max31790: revise the scale to write pwm
Thread-Index: AQHajIkmo9cWMbxIOkGH9cQc4G//sbFkmoSAgAWImEA=
Date: Tue, 16 Apr 2024 01:48:45 +0000
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> -----Original Message-----
> From: Guenter Roeck <groeck7@gmail.com> On Behalf Of Guenter Roeck
> Sent: Friday, April 12, 2024 9:03 PM
> To: Delphine_CC_Chiu/WYHQ/Wiwynn <Delphine_CC_Chiu@wiwynn.com>
> Cc: patrick@stwcx.xyz; Jean Delvare <jdelvare@suse.com>;
> linux-hwmon@vger.kernel.org; linux-kernel@vger.kernel.org
> Subject: Re: [PATCH v1] hwmon: max31790: revise the scale to write pwm
>=20
>   Security Reminder: Please be aware that this email is sent by an extern=
al
> sender.
>=20
> On Fri, Apr 12, 2024 at 11:25:58AM +0800, Delphine CC Chiu wrote:
> > Since the value for PWMOUT Target Duty Cycle register is a 9 bit
> > left-justified value that ranges from 0 to 511 and is contained in 2
> > bytes.
> >
> > There is an issue that the LSB of the 9 bit would always be zero if it
> > just left shift 8 bit for the value that write to PWMOUT Target Duty
> > Cycle register.
> >
> > Therefore, revise the scale of the value that was writen to pwm input
> > from 255 to 511 and modify the value to left-justified value.
> >
>=20
> The only difference is that it writes 511 instead of 510. All other value=
s are the
> same. I am not sure if that is really worth the trouble. It would have ma=
de a
> little more sense to me if you had used DIV_ROUND_CLOSEST(), but you didn=
't
> do that. As it is, I really don't understand the point. If it is really i=
mportant to
> write 511 instead of 510, the commit description should explain that and =
not
> talk about the last bit always being zero (which it still is after this p=
atch except,
> again, when writing 511 instead of 510).
>=20
> Thanks,
> Guenter
>=20
Hi Guenter,
Thanks for your reviewing.
I'll revise the code to use DIV_ROUND_CLOSEST().
The reason why we add this patch is that we saw an issue that the PWM signa=
l we get with oscilloscope would not be on consistently if we set PWM to 10=
0% to the driver, which would fail our hardware testing.
I'll describe more detail in the commit message.
Thanks.