From: Yingjoe Chen <yingjoe.chen@mediatek.com>
To: YH Huang <yh.huang@mediatek.com>
Cc: Thierry Reding <thierry.reding@gmail.com>,
Matthias Brugger <matthias.bgg@gmail.com>,
Mark Rutland <mark.rutland@arm.com>,
Rob Herring <robh+dt@kernel.org>, Pawel Moll <pawel.moll@arm.com>,
<linux-pwm@vger.kernel.org>, <devicetree@vger.kernel.org>,
<linux-kernel@vger.kernel.org>,
<linux-arm-kernel@lists.infradead.org>,
<srv_heupstream@mediatek.com>,
<linux-mediatek@lists.infradead.org>,
"Sascha Hauer" <kernel@pengutronix.de>
Subject: Re: [PATCH v2 2/2] pwm: add MediaTek display PWM driver support
Date: Thu, 18 Jun 2015 21:58:59 +0800 [thread overview]
Message-ID: <1434635939.22029.7.camel@mtksdaap41> (raw)
In-Reply-To: <1434622784.18278.39.camel@mtksdaap41>
On Thu, 2015-06-18 at 18:19 +0800, YH Huang wrote:
> On Fri, 2015-06-12 at 12:20 +0200, Thierry Reding wrote:
> > > +/* Shift log2(PWM_PERIOD_MAX + 1) as divisor */
> > > +#define PWM_PERIOD_BIT_SHIFT 12
> >
> > I wasn't very clear about this in my earlier review, so let me try to
> > explain why I think this is confusing. You use this as a divisor, but
> > you encode it as a shift. It's also PWM_PERIOD_MAX + 1, so I think it
> > would make more sense to drop this, keep PWM_PERIOD_MAX as above and
> > then replace the
> >
> > >> PWM_PERIOD_BIT_SHIFT
> >
> > below by
> >
> > / (PWM_PERIOD_MAX + 1)
> >
>
> Maybe I can change in this way:
> Remove this: #define PWM_PERIOD_MAX 0x00000fff
> Using ">> PWM_PERIOD_BIT_SHIFT" is faster than "/ (PWM_PERIOD_MAX + 1)"
> Is this right?
The place which use this shift is:
clk_div = div_u64(rate * period_ns, NSEC_PER_SEC) >>
PWM_PERIOD_BIT_SHIFT;
div_u64 return u64. If we change >> to /, and somehow compiler didn't
optimize that div into shift, it will cause build error.
Joe.C
WARNING: multiple messages have this Message-ID (diff)
From: Yingjoe Chen <yingjoe.chen@mediatek.com>
To: YH Huang <yh.huang@mediatek.com>
Cc: Thierry Reding <thierry.reding@gmail.com>,
Matthias Brugger <matthias.bgg@gmail.com>,
Mark Rutland <mark.rutland@arm.com>,
Rob Herring <robh+dt@kernel.org>, Pawel Moll <pawel.moll@arm.com>,
linux-pwm@vger.kernel.org, devicetree@vger.kernel.org,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
srv_heupstream@mediatek.com, linux-mediatek@lists.infradead.org,
Sascha Hauer <kernel@pengutronix.de>
Subject: Re: [PATCH v2 2/2] pwm: add MediaTek display PWM driver support
Date: Thu, 18 Jun 2015 21:58:59 +0800 [thread overview]
Message-ID: <1434635939.22029.7.camel@mtksdaap41> (raw)
In-Reply-To: <1434622784.18278.39.camel@mtksdaap41>
On Thu, 2015-06-18 at 18:19 +0800, YH Huang wrote:
> On Fri, 2015-06-12 at 12:20 +0200, Thierry Reding wrote:
> > > +/* Shift log2(PWM_PERIOD_MAX + 1) as divisor */
> > > +#define PWM_PERIOD_BIT_SHIFT 12
> >
> > I wasn't very clear about this in my earlier review, so let me try to
> > explain why I think this is confusing. You use this as a divisor, but
> > you encode it as a shift. It's also PWM_PERIOD_MAX + 1, so I think it
> > would make more sense to drop this, keep PWM_PERIOD_MAX as above and
> > then replace the
> >
> > >> PWM_PERIOD_BIT_SHIFT
> >
> > below by
> >
> > / (PWM_PERIOD_MAX + 1)
> >
>
> Maybe I can change in this way:
> Remove this: #define PWM_PERIOD_MAX 0x00000fff
> Using ">> PWM_PERIOD_BIT_SHIFT" is faster than "/ (PWM_PERIOD_MAX + 1)"
> Is this right?
The place which use this shift is:
clk_div = div_u64(rate * period_ns, NSEC_PER_SEC) >>
PWM_PERIOD_BIT_SHIFT;
div_u64 return u64. If we change >> to /, and somehow compiler didn't
optimize that div into shift, it will cause build error.
Joe.C
WARNING: multiple messages have this Message-ID (diff)
From: yingjoe.chen@mediatek.com (Yingjoe Chen)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2 2/2] pwm: add MediaTek display PWM driver support
Date: Thu, 18 Jun 2015 21:58:59 +0800 [thread overview]
Message-ID: <1434635939.22029.7.camel@mtksdaap41> (raw)
In-Reply-To: <1434622784.18278.39.camel@mtksdaap41>
On Thu, 2015-06-18 at 18:19 +0800, YH Huang wrote:
> On Fri, 2015-06-12 at 12:20 +0200, Thierry Reding wrote:
> > > +/* Shift log2(PWM_PERIOD_MAX + 1) as divisor */
> > > +#define PWM_PERIOD_BIT_SHIFT 12
> >
> > I wasn't very clear about this in my earlier review, so let me try to
> > explain why I think this is confusing. You use this as a divisor, but
> > you encode it as a shift. It's also PWM_PERIOD_MAX + 1, so I think it
> > would make more sense to drop this, keep PWM_PERIOD_MAX as above and
> > then replace the
> >
> > >> PWM_PERIOD_BIT_SHIFT
> >
> > below by
> >
> > / (PWM_PERIOD_MAX + 1)
> >
>
> Maybe I can change in this way:
> Remove this: #define PWM_PERIOD_MAX 0x00000fff
> Using ">> PWM_PERIOD_BIT_SHIFT" is faster than "/ (PWM_PERIOD_MAX + 1)"
> Is this right?
The place which use this shift is:
clk_div = div_u64(rate * period_ns, NSEC_PER_SEC) >>
PWM_PERIOD_BIT_SHIFT;
div_u64 return u64. If we change >> to /, and somehow compiler didn't
optimize that div into shift, it will cause build error.
Joe.C
next prev parent reply other threads:[~2015-06-18 13:59 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-21 13:29 [PATCH v2 0/2] Add MediaTek display PWM driver YH Huang
2015-05-21 13:29 ` YH Huang
2015-05-21 13:29 ` YH Huang
2015-05-21 13:29 ` [PATCH v2 1/2] dt-bindings: pwm: add MediaTek display PWM bindings YH Huang
2015-05-21 13:29 ` YH Huang
2015-05-21 13:29 ` YH Huang
2015-06-12 10:23 ` Thierry Reding
2015-06-12 10:23 ` Thierry Reding
2015-06-18 9:00 ` YH Huang
2015-06-18 9:00 ` YH Huang
2015-06-18 9:00 ` YH Huang
2015-05-21 13:29 ` [PATCH v2 2/2] pwm: add MediaTek display PWM driver support YH Huang
2015-05-21 13:29 ` YH Huang
2015-05-21 13:29 ` YH Huang
2015-06-12 10:20 ` Thierry Reding
2015-06-12 10:20 ` Thierry Reding
2015-06-18 10:19 ` YH Huang
2015-06-18 10:19 ` YH Huang
2015-06-18 10:19 ` YH Huang
2015-06-18 13:58 ` Yingjoe Chen [this message]
2015-06-18 13:58 ` Yingjoe Chen
2015-06-18 13:58 ` Yingjoe Chen
2015-06-29 9:27 ` Thierry Reding
2015-06-29 9:27 ` Thierry Reding
2015-06-29 9:21 ` Thierry Reding
2015-06-29 9:21 ` Thierry Reding
2015-06-12 10:25 ` Thierry Reding
2015-06-12 10:25 ` Thierry Reding
2015-06-18 9:02 ` YH Huang
2015-06-18 9:02 ` YH Huang
2015-06-18 9:02 ` YH Huang
2015-05-25 2:14 ` [PATCH v2 0/2] Add MediaTek display PWM driver Yingjoe Chen
2015-05-25 2:14 ` Yingjoe Chen
2015-05-25 2:14 ` Yingjoe Chen
2015-06-05 6:15 ` YH Huang
2015-06-05 6:15 ` YH Huang
2015-06-05 8:39 ` Matthias Brugger
2015-06-05 8:39 ` Matthias Brugger
2015-06-05 10:45 ` YH Huang
2015-06-05 10:45 ` YH Huang
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