From: Sascha Hauer <s.hauer@pengutronix.de>
To: Alexander Shiyan <shc_work@mail.ru>
Cc: linux-kernel@vger.kernel.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
devel@driverdev.osuosl.org, linux-arm-kernel@lists.infradead.org,
Shawn Guo <shawn.guo@linaro.org>,
Philipp Zabel <p.zabel@pengutronix.de>
Subject: Re: [RFC] Staging: imx-drm: Do not use fractional part of divider
Date: Mon, 17 Jun 2013 10:48:44 +0200 [thread overview]
Message-ID: <20130617084844.GP32299@pengutronix.de> (raw)
In-Reply-To: <1371195670.904413971@f400.i.mail.ru>
On Fri, Jun 14, 2013 at 11:41:10AM +0400, Alexander Shiyan wrote:
> Hello.
>
> Analysis of driver imx-drm led me to believe that the use fractional part of the divider is not always a good idea.
> For example, for a parallel display bus connected to LVDS converter chip (DS90C363), in this case the use of
> fractional part, clock will unstable and the on-chip PLL is not working properly, or rather, does not work at all.
>
> Let me give a specific example.
> ipu_crtc_mode_set 0x36314752
> imx-ipuv3 40000000.ipu: clk_di_round_rate: inrate: 133000000 div: 0x00000035 outrate: 40150928 wanted: 40000000
> imx-ipuv3 40000000.ipu: clk_di_round_rate: inrate: 133000000 div: 0x00000035 outrate: 40150928 wanted: 40150928
> imx-ipuv3 40000000.ipu: clk_di_set_rate: inrate: 133000000 desired: 40150928 div: 0x00000035
>
> In this case the divider is 3.5, that result to clock is incorrect. See an attached oscillogram F0000TEK.jpg.
>
> After a patch the clocks is OK. Patch just uncomment some FSL code.
> imx-ipuv3 40000000.ipu: clk_di_round_rate: inrate: 133000000 div: 0x00000040 outrate: 33250000 wanted: 40000000
> imx-ipuv3 40000000.ipu: clk_di_round_rate: inrate: 133000000 div: 0x00000040 outrate: 33250000 wanted: 33250000
> imx-ipuv3 40000000.ipu: clk_di_set_rate: inrate: 133000000 desired: 33250000 div: 0x00000040
>
> See an attached oscillogram F0001TEK.jpg.
>
> So, I want to review this from developers and wait for comments.
>
We may need some flag in the devicetree to specify whether the
fractional divider can be used or not.
Sascha
--
Pengutronix e.K. | |
Industrial Linux Solutions | http://www.pengutronix.de/ |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 |
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WARNING: multiple messages have this Message-ID (diff)
From: s.hauer@pengutronix.de (Sascha Hauer)
To: linux-arm-kernel@lists.infradead.org
Subject: [RFC] Staging: imx-drm: Do not use fractional part of divider
Date: Mon, 17 Jun 2013 10:48:44 +0200 [thread overview]
Message-ID: <20130617084844.GP32299@pengutronix.de> (raw)
In-Reply-To: <1371195670.904413971@f400.i.mail.ru>
On Fri, Jun 14, 2013 at 11:41:10AM +0400, Alexander Shiyan wrote:
> Hello.
>
> Analysis of driver imx-drm led me to believe that the use fractional part of the divider is not always a good idea.
> For example, for a parallel display bus connected to LVDS converter chip (DS90C363), in this case the use of
> fractional part, clock will unstable and the on-chip PLL is not working properly, or rather, does not work at all.
>
> Let me give a specific example.
> ipu_crtc_mode_set 0x36314752
> imx-ipuv3 40000000.ipu: clk_di_round_rate: inrate: 133000000 div: 0x00000035 outrate: 40150928 wanted: 40000000
> imx-ipuv3 40000000.ipu: clk_di_round_rate: inrate: 133000000 div: 0x00000035 outrate: 40150928 wanted: 40150928
> imx-ipuv3 40000000.ipu: clk_di_set_rate: inrate: 133000000 desired: 40150928 div: 0x00000035
>
> In this case the divider is 3.5, that result to clock is incorrect. See an attached oscillogram F0000TEK.jpg.
>
> After a patch the clocks is OK. Patch just uncomment some FSL code.
> imx-ipuv3 40000000.ipu: clk_di_round_rate: inrate: 133000000 div: 0x00000040 outrate: 33250000 wanted: 40000000
> imx-ipuv3 40000000.ipu: clk_di_round_rate: inrate: 133000000 div: 0x00000040 outrate: 33250000 wanted: 33250000
> imx-ipuv3 40000000.ipu: clk_di_set_rate: inrate: 133000000 desired: 33250000 div: 0x00000040
>
> See an attached oscillogram F0001TEK.jpg.
>
> So, I want to review this from developers and wait for comments.
>
We may need some flag in the devicetree to specify whether the
fractional divider can be used or not.
Sascha
--
Pengutronix e.K. | |
Industrial Linux Solutions | http://www.pengutronix.de/ |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
next prev parent reply other threads:[~2013-06-17 8:48 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-14 7:41 [RFC] Staging: imx-drm: Do not use fractional part of divider Alexander Shiyan
2013-06-14 7:41 ` Alexander Shiyan
2013-06-14 23:23 ` Jiada Wang
2013-06-14 23:23 ` Jiada Wang
2013-06-17 8:48 ` Sascha Hauer [this message]
2013-06-17 8:48 ` Sascha Hauer
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