Messages in this thread | | | Date | Tue, 8 Aug 2006 05:57:30 -0700 (PDT) | From | Komal Shah <> | Subject | Re: [PATCH] OMAP: I2C driver for TI OMAP boards #3 |
| |
--- Tony Lindgren <tony@atomide.com> wrote:
> Hi, > > * Jean Delvare <khali@linux-fr.org> [060805 11:31]: > > > > > >> + if (armxor_rate > 16000000) > > > >> + psc = (armxor_rate + 8000000) / 12000000; > > > >> + else > > > >> + psc = 0; > > > > > > >Can you please explain this formula? > > > > > > The OMAP core uses 8-bit value to divide the system clock (SCLK) > and > > > generates its own sampling clock (ICLK), and the core logic is > sampled > > > at clock rate of the system clock for the module, divided by > (prescaler value + 1) > > > > I should have been more precise, I guess. What surprises me are the > > numbers themselves. It's frequent to see forumlae of the form > > "a = (b + c/2) / c" to divide with proper rounding, but here you > have > > 2c/3 instread of c/2. My question was more like: is it intentional, > or a > > typo? Also, with the code above, psc will never have value 1. The > "if" > > part will always compute to at least 2, and the "else" part to 0. > Is > > this OK? > > > > Hmmm, this sounds like a bug somewhere. TRM for 5912 says the I2C > clock > must be prescaled to be between 7 - 12 MHz [1]. The XOR input clock > is > typically 12, 13 or 19.2 MHz. So we should have code that produces: > > XOR Mhz Divider Prescaler > 12 1 0 > 13 2 1 > 19.2 2 1 > > Then again the original old code produces something different too > [2]... > > I suspect the original code had some hw workarounds and and later > code > may have a conversion bug somewhere :) > > I suggest we keep the code as is for now since it's known to work on > all omaps, and then submit a follow-up patch later once we have > verified that that code based on the TRM works on all omaps.
I have updated the driver with all other review comments except comment on formula above by Jean. I can some part of description from Tony's explanation along with removing the following code line
/* Set Own Address */ omap_i2c_write_reg(dev, OMAP_I2C_OA_REG, dev->own_address); As it is not needed. Please confirm so that I can send the revised patch soon.
---Komal Shah http://komalshah.blogspot.com/
__________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |