From mboxrd@z Thu Jan 1 00:00:00 1970 From: Aaron Brice Subject: Re: [PATCH v1 0/2] spi: fsl-dspi: better approximation for baudrate Date: Fri, 03 Apr 2015 10:50:46 -0700 Message-ID: <551ED2F6.8020701@datasoft.com> References: <1427965907-28125-1-git-send-email-andy.shevchenko@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit To: Andy Shevchenko , linux-spi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Mark Brown Return-path: In-Reply-To: <1427965907-28125-1-git-send-email-andy.shevchenko-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Sender: linux-spi-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Andy, See comments below. On 04/02/2015 02:11 AM, Andy Shevchenko wrote: > This series makes better approximation when baud rate divisor parameters are > calculated. > > The algorithm is represent as Python script here [1]. First parameter is > algorithm (0 - original, 1 - after patch 1/2, 2 - after patch 2/2, 3 - memory > vs. performance: use precalculated scales). > > I played with let's say standard baud rates (which I used for Quark) and > separately run algorithms 0 and 1 for range 100-5000 baud. Input frequency is > 64MHz. It seems my algo shows better results in all cases. Here is a diff for > 'standard' baud rates > (speed_hz, DBR, i, BR, j, PBR, real baud rate, difference): > > --- result0 2015-04-02 00:38:48.845761004 +0300 > +++ result1 2015-04-02 00:38:48.913760154 +0300 > @@ -5,7 +5,7 @@ > 25000000 0 0 2 0 2 16000000 9000000 > 20000000 0 0 2 0 2 16000000 4000000 > 16667000 0 0 2 0 2 16000000 667000 > -13333000 0 0 2 0 2 16000000 2667000 > +13333000 0 0 2 1 3 10666666 2666334 This one is definitely a bug in the original due to dropping the remainder in the 4.8 scale factor needed. > 12500000 0 0 2 1 3 10666666 1833334 > 10000000 0 0 2 1 3 10666666 666666 > 8000000 0 1 4 0 2 8000000 0 > @@ -17,36 +17,36 @@ > 3140500 0 1 4 2 5 3200000 59500 > 3125000 0 1 4 2 5 3200000 75000 > 3109500 0 1 4 2 5 3200000 90500 > -2500000 0 1 4 3 7 2285714 214286 > +2500000 0 3 8 1 3 2666666 166666 The rest of these I'm not sure about. The property is called "spi-max-frequency" and the description in the bindings document is: - spi-max-frequency - (required) Maximum SPI clocking speed of device in Hz In the rest of the examples you've gotten a closer baud rate by exceeding the "Maximum" value. I don't think you want best approximation, I think you want closest without going over.. > 2000000 0 4 16 0 2 2000000 0 > 1563000 0 3 8 2 5 1600000 37000 > -1250000 0 3 8 3 7 1142857 107143 > +1250000 0 4 16 1 3 1333333 83333 > 1006000 0 5 32 0 2 1000000 6000 > 1000000 0 5 32 0 2 1000000 0 > 994000 0 5 32 0 2 1000000 6000 > 800000 0 4 16 2 5 800000 0 > -781250 0 5 32 1 3 666666 114584 > -625000 0 4 16 3 7 571428 53572 > +781250 0 4 16 2 5 800000 18750 > +625000 0 5 32 1 3 666666 41666 > 500000 0 6 64 0 2 500000 0 > 400000 0 5 32 2 5 400000 0 > -390625 0 6 64 1 3 333333 57292 > +390625 0 5 32 2 5 400000 9375 > 250000 0 7 128 0 2 250000 0 > 200000 0 6 64 2 5 200000 0 > 205313 0 6 64 2 5 200000 5313 > -195313 0 7 128 1 3 166666 28647 > -185313 0 7 128 1 3 166666 18647 > +195313 0 6 64 2 5 200000 4687 > +185313 0 6 64 2 5 200000 14687 > 125000 0 8 256 0 2 125000 0 > 100700 0 7 128 2 5 100000 700 > 100000 0 7 128 2 5 100000 0 > -99300 0 8 256 1 3 83333 15967 > +99300 0 7 128 2 5 100000 700 > 50000 0 8 256 2 5 50000 0 > 25000 0 9 512 2 5 25000 0 > -10066 0 10 1024 3 7 8928 1138 > -10016 0 10 1024 3 7 8928 1088 > -9966 0 10 1024 3 7 8928 1038 > -5065 0 11 2048 3 7 4464 601 > -5040 0 11 2048 3 7 4464 576 > -5015 0 11 2048 3 7 4464 551 > +10066 0 11 2048 1 3 10416 350 > +10016 0 11 2048 1 3 10416 400 > +9966 0 11 2048 1 3 10416 450 > +5065 0 12 4096 1 3 5208 143 > +5040 0 12 4096 1 3 5208 168 > +5015 0 12 4096 1 3 5208 193 > 1007 0 15 32768 0 2 976 31 > 1002 0 15 32768 0 2 976 26 > 997 0 15 32768 0 2 976 21 > > Patch 2 is RFC, since I don't know if all DSPI modules has that bit (at least > what I found on public for MC55xx) and how duty cycle is significant. > > Not compiled. Not tested. > > [1] http://pastebin.com/uy0CKc6b > > Andy Shevchenko (2): > spi: fsl-dspi: increase precision of baud rate approximation > spi: fsl-dspi: use double baud rate in approximation > > drivers/spi/spi-fsl-dspi.c | 50 +++++++++++++++++++++------------------------- > 1 file changed, 23 insertions(+), 27 deletions(-) > Thanks, Aaron -- To unsubscribe from this list: send the line "unsubscribe linux-spi" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html