On Tue, 2018-11-20 at 01:28 +0100, Anatolij Gustschin wrote:
> Add USB interface driver for ARRI FPGA configuration devices based on
> FTDI FT232H chip. Depending on USB PID the driver registers different
> platform devices describing an FPGA configuration interface.
Is ARRI different than Arria?
> +/* Use baudrate calculation borrowed from libftdi */
> +static int ftdi_to_clkbits(int baudrate, unsigned int clk, int clk_div,
Linux uses unsigned values for clocks. Does it make any sense to mix
the unsigned clk with signed values? Seems like baudrate and clk_div
should also be unsigned.
> + unsigned long *encoded_divisor)
unsigned long is an odd choice here. Is there any to reason to use an
unsigned long to store the result of right shifting a signed int
(best_div)? It can't be longer than a int, but it can be negative.
> +{
> + static const char frac_code[8] = { 0, 3, 2, 4, 1, 5, 6, 7 };
> + int best_baud = 0;
> + int div, best_div;
> +
> + if (baudrate >= clk / clk_div) {
> + *encoded_divisor = 0;
> + best_baud = clk / clk_div;
> + } else if (baudrate >= clk / (clk_div + clk_div / 2)) {
> + *encoded_divisor = 1;
> + best_baud = clk / (clk_div + clk_div / 2);
> + } else if (baudrate >= clk / (2 * clk_div)) {
> + *encoded_divisor = 2;
> + best_baud = clk / (2 * clk_div);
> + } else {
> + /*
> + * Divide by 16 to have 3 fractional bits and
> + * one bit for rounding
> + */
> + div = clk * 16 / clk_div / baudrate;
>
> + if (div & 1) /* Decide if to round up or down */
> + best_div = div / 2 + 1;
> + else
> + best_div = div / 2;
In Linux we would write:
best_div = DIV_ROUND_UP(div, 2);
Though I think you can combine that with the above to get:
best_div = DIV_ROUND_CLOSEST(clk * 8 / clk_div, baudrate);
That what the above is trying to accomplish in a round about way
> + if (best_div > 0x20000)
> + best_div = 0x1ffff;
Looks like the above was probably supposed to be >=
> + best_baud = clk * 16 / clk_div / best_div;
> + if (best_baud & 1) /* Decide if to round up or down */
> + best_baud = best_baud / 2 + 1;
> + else
> + best_baud = best_baud / 2;
Again, looks like a complicated way to round to the nearest.
> + *encoded_divisor = (best_div >> 3) |
> + (frac_code[best_div & 0x7] << 14);
> + }
> + return best_baud;
>
