2016-11-28 8:58 GMT+01:00 Sekhar Nori <nsekhar@xxxxxx>: > On Monday 28 November 2016 01:12 PM, Tomi Valkeinen wrote: >> On 28/11/16 07:24, Sekhar Nori wrote: >>> On Friday 25 November 2016 09:07 PM, Bartosz Golaszewski wrote: >>>> It has been determined that the maximum resolution supported correctly >>>> by tilcdc rev1 on da850 SoCs is 800x600@60. Due to memory throughput >>>> constraints we must filter out higher modes. >>>> >>>> Specify the max-bandwidth property for the display node for >>>> da850-based boards. >>>> >>>> Signed-off-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx> >>>> --- >>>> arch/arm/boot/dts/da850.dtsi | 1 + >>>> 1 file changed, 1 insertion(+) >>>> >>>> diff --git a/arch/arm/boot/dts/da850.dtsi b/arch/arm/boot/dts/da850.dtsi >>>> index 8e30d9b..9b7c444 100644 >>>> --- a/arch/arm/boot/dts/da850.dtsi >>>> +++ b/arch/arm/boot/dts/da850.dtsi >>>> @@ -452,6 +452,7 @@ >>>> compatible = "ti,da850-tilcdc"; >>>> reg = <0x213000 0x1000>; >>>> interrupts = <52>; >>>> + max-bandwidth = <28800000>; >>> >>> If this is effectively the max pixel clock that the device supports, >>> then why not use the datasheet specified value of 37.5 MHz (Tc = 26.66 ns). >> >> There's a separate property for max-pixelclock. This one is maximum >> pixels per second (which does sound almost the same), but the doc says >> it's about the particular memory interface + LCDC combination. > > DA850 supports both mDDR and DDR2, at slightly different speeds. So > memory bandwidth limitation is also board specific. This should probably > move to board file. > > But I would like to know why using max-pixelclock is not good enough. > Have experiments shown that LCDC on DA850 LCDK underflows even if pixel > clock is below the datasheet recommendation? > Hi Sekhar, I've just tested 1024x768 at 37000 KHz - indeed seems like the underflows are gone as soon as we go below 37500 KHz. I'll submit a new patch using the max-pixelclock property. Thanks, Bartosz Golaszewski -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
