From: Thierry Reding <thierry.reding@gmail.com> To: YH Huang <yh.huang@mediatek.com> Cc: 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>, yingjoe.chen@mediatek.com Subject: Re: [PATCH v2 2/2] pwm: add MediaTek display PWM driver support Date: Mon, 29 Jun 2015 11:21:47 +0200 [thread overview] Message-ID: <20150629092145.GF5431@ulmo> (raw) In-Reply-To: <1434622784.18278.39.camel@mtksdaap41> [-- Attachment #1: Type: text/plain, Size: 1378 bytes --] On Thu, Jun 18, 2015 at 06:19:44PM +0800, YH Huang wrote: > On Fri, 2015-06-12 at 12:20 +0200, Thierry Reding wrote: > > On Thu, May 21, 2015 at 09:29:24PM +0800, YH Huang wrote: [...] > > > +#define DISP_PWM_CON_1 0x14 > > > +#define PWM_PERIOD_MASK 0xfff > > > +#define PWM_PERIOD_MAX 0x00000fff > > > > Same here. PWM_PERIOD_MAX isn't actually used anywhere, so perhaps just > > drop it altogether. But see also below... > > > > > +/* 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 compiler should be able to optimize the division to a shift, so both will likely result in the same code. But I don't mind much either way as long as we don't define two symbols for essentially the same value. Thierry [-- Attachment #2: Type: application/pgp-signature, Size: 819 bytes --]
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From: thierry.reding@gmail.com (Thierry Reding) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH v2 2/2] pwm: add MediaTek display PWM driver support Date: Mon, 29 Jun 2015 11:21:47 +0200 [thread overview] Message-ID: <20150629092145.GF5431@ulmo> (raw) In-Reply-To: <1434622784.18278.39.camel@mtksdaap41> On Thu, Jun 18, 2015 at 06:19:44PM +0800, YH Huang wrote: > On Fri, 2015-06-12 at 12:20 +0200, Thierry Reding wrote: > > On Thu, May 21, 2015 at 09:29:24PM +0800, YH Huang wrote: [...] > > > +#define DISP_PWM_CON_1 0x14 > > > +#define PWM_PERIOD_MASK 0xfff > > > +#define PWM_PERIOD_MAX 0x00000fff > > > > Same here. PWM_PERIOD_MAX isn't actually used anywhere, so perhaps just > > drop it altogether. But see also below... > > > > > +/* 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 compiler should be able to optimize the division to a shift, so both will likely result in the same code. But I don't mind much either way as long as we don't define two symbols for essentially the same value. Thierry -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 819 bytes Desc: not available URL: <http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20150629/bf3a6421/attachment.sig>
next prev parent reply other threads:[~2015-06-29 9:23 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 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 [this message] 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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