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Tue, 10 Dec 2019 14:11:40 +0000 Received: from DB3PR0202MB3434.eurprd02.prod.outlook.com ([fe80::446e:c4f8:7e59:1c6d]) by DB3PR0202MB3434.eurprd02.prod.outlook.com ([fe80::446e:c4f8:7e59:1c6d%7]) with mapi id 15.20.2516.018; Tue, 10 Dec 2019 14:11:40 +0000 From: Peter Rosin To: Claudiu Beznea , "sam@ravnborg.org" , "bbrezillon@kernel.org" , "airlied@linux.ie" , "daniel@ffwll.ch" , "nicolas.ferre@microchip.com" , "alexandre.belloni@bootlin.com" , "ludovic.desroches@microchip.com" , "lee.jones@linaro.org" Subject: Re: [PATCH 4/5] Revert "drm/atmel-hlcdc: allow selecting a higher pixel-clock than requested" Thread-Topic: [PATCH 4/5] Revert "drm/atmel-hlcdc: allow selecting a higher pixel-clock than requested" Thread-Index: AQHVr11DyxIz9S+dLEWyrkArJlSyg6ezaL2A Date: Tue, 10 Dec 2019 14:11:40 +0000 Message-ID: <4c3ffc48-7aa5-1e48-b0e9-a50c4eea7c38@axentia.se> References: <1575984287-26787-1-git-send-email-claudiu.beznea@microchip.com> <1575984287-26787-5-git-send-email-claudiu.beznea@microchip.com> In-Reply-To: <1575984287-26787-5-git-send-email-claudiu.beznea@microchip.com> Accept-Language: en-US, sv-SE Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: user-agent: Mozilla/5.0 (Windows NT 10.0; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2019-12-10 14:24, Claudiu Beznea wrote: > This reverts commit f6f7ad3234613f6f7f27c25036aaf078de07e9b0. > ("drm/atmel-hlcdc: allow selecting a higher pixel-clock than requested") > because allowing selecting a higher pixel clock may overclock > LCD devices, not all of them being capable of this. Without this patch, there are panels that are *severly* underclocked (on the magnitude of 40MHz instead of 65MHz or something like that, I don't remember the exact figures). And they are of course not capable of that. All panels have *some* slack as to what frequencies are supported, and the patch was written under the assumption that the preferred frequency of the panel was requested, which should leave at least a *little* headroom. So, I'm curious as to what panel regressed. Or rather, what pixel-clock it needs and what it gets with/without the patch? Or is the revert based on some theory of a perceived risk of toasting a panel? In short, this revert regresses my use case and I would like at least a hook to re-enable the removed logic. Cheers, Peter > Cc: Peter Rosin > Signed-off-by: Claudiu Beznea > --- > drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c | 12 ------------ > 1 file changed, 12 deletions(-) > > diff --git a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c > index 721fa88bf71d..1a70dff1a417 100644 > --- a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c > +++ b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c > @@ -117,18 +117,6 @@ static void atmel_hlcdc_crtc_mode_set_nofb(struct drm_crtc *c) > div = DIV_ROUND_UP(prate, mode_rate); > if (ATMEL_HLCDC_CLKDIV(div) & ~ATMEL_HLCDC_CLKDIV_MASK) > div = ATMEL_HLCDC_CLKDIV_MASK; > - } else { > - int div_low = prate / mode_rate; > - > - if (div_low >= 2 && > - ((prate / div_low - mode_rate) < > - 10 * (mode_rate - prate / div))) > - /* > - * At least 10 times better when using a higher > - * frequency than requested, instead of a lower. > - * So, go with that. > - */ > - div = div_low; > } > > cfg |= ATMEL_HLCDC_CLKDIV(div); > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel