| Message ID | 1657221457-32494-1-git-send-email-quic_vnivarth@quicinc.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [V3] tty: serial: qcom-geni-serial: Fix get_clk_div_rate() which otherwise could return a sub-optimal clock rate. | expand |
On 7/8/2022 6:41 PM, Greg KH wrote: > On Fri, Jul 08, 2022 at 12:47:37AM +0530, Vijaya Krishna Nivarthi wrote: >> In the logic around call to clk_round_rate(), for some corner conditions, >> get_clk_div_rate() could return an sub-optimal clock rate. Also, if an >> exact clock rate was not found lowest clock was being returned. >> >> Search for suitable clock rate in 2 steps >> a) exact match or within 2% tolerance >> b) within 5% tolerance >> This also takes care of corner conditions. >> >> Fixes: c2194bc999d4 ("tty: serial: qcom-geni-serial: Remove uart frequency table. Instead, find suitable frequency with call to clk_round_rate") >> Signed-off-by: Vijaya Krishna Nivarthi <quic_vnivarth@quicinc.com> >> --- >> v3: simplified algorithm further, fixed robot compile warnings >> v2: removed minor optimisations to make more readable >> v1: intial patch contained slightly complicated logic >> --- >> drivers/tty/serial/qcom_geni_serial.c | 88 +++++++++++++++++++++-------------- >> 1 file changed, 53 insertions(+), 35 deletions(-) >> >> diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c >> index 2e23b65..ac2df1c 100644 >> --- a/drivers/tty/serial/qcom_geni_serial.c >> +++ b/drivers/tty/serial/qcom_geni_serial.c >> @@ -943,52 +943,71 @@ static int qcom_geni_serial_startup(struct uart_port *uport) >> return 0; >> } >> >> -static unsigned long get_clk_div_rate(struct clk *clk, unsigned int baud, >> - unsigned int sampling_rate, unsigned int *clk_div) >> +static unsigned long find_clk_rate_in_tol(struct clk *clk, unsigned int desired_clk, >> + unsigned int *clk_div, unsigned int percent_tol) >> { >> - unsigned long ser_clk; >> - unsigned long desired_clk; >> - unsigned long freq, prev; >> + unsigned long freq; >> unsigned long div, maxdiv; >> - int64_t mult; >> - >> - desired_clk = baud * sampling_rate; >> - if (!desired_clk) { >> - pr_err("%s: Invalid frequency\n", __func__); >> - return 0; >> - } >> + u64 mult; >> + unsigned long offset, abs_tol, achieved; >> >> + abs_tol = div_u64((u64)desired_clk * percent_tol, 100); >> maxdiv = CLK_DIV_MSK >> CLK_DIV_SHFT; >> - prev = 0; >> - >> - for (div = 1; div <= maxdiv; div++) { >> - mult = div * desired_clk; >> - if (mult > ULONG_MAX) >> + div = 1; >> + while (div <= maxdiv) { >> + mult = (u64)div * desired_clk; >> + if (mult != (unsigned long)mult) >> break; >> >> - freq = clk_round_rate(clk, (unsigned long)mult); >> - if (!(freq % desired_clk)) { >> - ser_clk = freq; >> - break; >> - } >> + offset = div * abs_tol; >> + freq = clk_round_rate(clk, mult - offset); >> >> - if (!prev) >> - ser_clk = freq; >> - else if (prev == freq) >> + /* Can only get lower if we're done */ >> + if (freq < mult - offset) >> break; >> >> - prev = freq; >> + /* >> + * Re-calculate div in case rounding skipped rates but we >> + * ended up at a good one, then check for a match. >> + */ >> + div = DIV_ROUND_CLOSEST(freq, desired_clk); >> + achieved = DIV_ROUND_CLOSEST(freq, div); >> + if (achieved <= desired_clk + abs_tol && >> + achieved >= desired_clk - abs_tol) { >> + *clk_div = div; >> + return freq; >> + } >> + >> + div = DIV_ROUND_UP(freq, desired_clk); >> } >> >> - if (!ser_clk) { >> - pr_err("%s: Can't find matching DFS entry for baud %d\n", >> - __func__, baud); >> - return ser_clk; >> + return 0; >> +} >> + >> +static unsigned long get_clk_div_rate(struct clk *clk, unsigned int baud, >> + unsigned int sampling_rate, unsigned int *clk_div) >> +{ >> + unsigned long ser_clk; >> + unsigned long desired_clk; >> + >> + desired_clk = baud * sampling_rate; >> + if (!desired_clk) { >> + pr_err("%s: Invalid frequency\n", __func__); > Note, this is a driver, ALWAYS use dev_err() and friends instead. > > Also do not allow userspace to flood the kernel logs like this looks is > possible, this should just be dev_dbg(). > > And of course, never use __func__, it's not needed anymore for > dev_dbg(). Ok. > >> + return 0; > Why if you have a error, are you returning 0? Yes, and it has been so earlier too. 0 is an invalid clock rate and will be handled accordingly by caller. >> } >> >> - *clk_div = ser_clk / desired_clk; >> - if (!(*clk_div)) >> - *clk_div = 1; >> + /* >> + * try to find a clock rate within 2% tolerance, then within >> + */ >> + ser_clk = find_clk_rate_in_tol(clk, desired_clk, clk_div, 2); >> + if (!ser_clk) >> + ser_clk = find_clk_rate_in_tol(clk, desired_clk, clk_div, 5); >> + >> + if (!ser_clk) >> + pr_err("Couldn't find suitable clock rate for %lu\n", desired_clk); > return an error? > > dev_err(). As mentioned, we didn't (and don't) return error from here but 0. > >> + else >> + pr_debug("desired_clk-%lu, ser_clk-%lu, clk_div-%lu\n", >> + desired_clk, ser_clk, *clk_div); > dev_dbg()? Ok. > > Also, as the kernel test robot says, this does not build cleanly :( change to dev_dbg should take care of these. Will do. Thank you. Vijay/ > > thanks, > > greg k-h
diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c index 2e23b65..ac2df1c 100644 --- a/drivers/tty/serial/qcom_geni_serial.c +++ b/drivers/tty/serial/qcom_geni_serial.c @@ -943,52 +943,71 @@ static int qcom_geni_serial_startup(struct uart_port *uport) return 0; } -static unsigned long get_clk_div_rate(struct clk *clk, unsigned int baud, - unsigned int sampling_rate, unsigned int *clk_div) +static unsigned long find_clk_rate_in_tol(struct clk *clk, unsigned int desired_clk, + unsigned int *clk_div, unsigned int percent_tol) { - unsigned long ser_clk; - unsigned long desired_clk; - unsigned long freq, prev; + unsigned long freq; unsigned long div, maxdiv; - int64_t mult; - - desired_clk = baud * sampling_rate; - if (!desired_clk) { - pr_err("%s: Invalid frequency\n", __func__); - return 0; - } + u64 mult; + unsigned long offset, abs_tol, achieved; + abs_tol = div_u64((u64)desired_clk * percent_tol, 100); maxdiv = CLK_DIV_MSK >> CLK_DIV_SHFT; - prev = 0; - - for (div = 1; div <= maxdiv; div++) { - mult = div * desired_clk; - if (mult > ULONG_MAX) + div = 1; + while (div <= maxdiv) { + mult = (u64)div * desired_clk; + if (mult != (unsigned long)mult) break; - freq = clk_round_rate(clk, (unsigned long)mult); - if (!(freq % desired_clk)) { - ser_clk = freq; - break; - } + offset = div * abs_tol; + freq = clk_round_rate(clk, mult - offset); - if (!prev) - ser_clk = freq; - else if (prev == freq) + /* Can only get lower if we're done */ + if (freq < mult - offset) break; - prev = freq; + /* + * Re-calculate div in case rounding skipped rates but we + * ended up at a good one, then check for a match. + */ + div = DIV_ROUND_CLOSEST(freq, desired_clk); + achieved = DIV_ROUND_CLOSEST(freq, div); + if (achieved <= desired_clk + abs_tol && + achieved >= desired_clk - abs_tol) { + *clk_div = div; + return freq; + } + + div = DIV_ROUND_UP(freq, desired_clk); } - if (!ser_clk) { - pr_err("%s: Can't find matching DFS entry for baud %d\n", - __func__, baud); - return ser_clk; + return 0; +} + +static unsigned long get_clk_div_rate(struct clk *clk, unsigned int baud, + unsigned int sampling_rate, unsigned int *clk_div) +{ + unsigned long ser_clk; + unsigned long desired_clk; + + desired_clk = baud * sampling_rate; + if (!desired_clk) { + pr_err("%s: Invalid frequency\n", __func__); + return 0; } - *clk_div = ser_clk / desired_clk; - if (!(*clk_div)) - *clk_div = 1; + /* + * try to find a clock rate within 2% tolerance, then within + */ + ser_clk = find_clk_rate_in_tol(clk, desired_clk, clk_div, 2); + if (!ser_clk) + ser_clk = find_clk_rate_in_tol(clk, desired_clk, clk_div, 5); + + if (!ser_clk) + pr_err("Couldn't find suitable clock rate for %lu\n", desired_clk); + else + pr_debug("desired_clk-%lu, ser_clk-%lu, clk_div-%lu\n", + desired_clk, ser_clk, *clk_div); return ser_clk; } @@ -1021,8 +1040,7 @@ static void qcom_geni_serial_set_termios(struct uart_port *uport, if (ver >= QUP_SE_VERSION_2_5) sampling_rate /= 2; - clk_rate = get_clk_div_rate(port->se.clk, baud, - sampling_rate, &clk_div); + clk_rate = get_clk_div_rate(port->se.clk, baud, sampling_rate, &clk_div); if (!clk_rate) goto out_restart_rx;
In the logic around call to clk_round_rate(), for some corner conditions, get_clk_div_rate() could return an sub-optimal clock rate. Also, if an exact clock rate was not found lowest clock was being returned. Search for suitable clock rate in 2 steps a) exact match or within 2% tolerance b) within 5% tolerance This also takes care of corner conditions. Fixes: c2194bc999d4 ("tty: serial: qcom-geni-serial: Remove uart frequency table. Instead, find suitable frequency with call to clk_round_rate") Signed-off-by: Vijaya Krishna Nivarthi <quic_vnivarth@quicinc.com> --- v3: simplified algorithm further, fixed robot compile warnings v2: removed minor optimisations to make more readable v1: intial patch contained slightly complicated logic --- drivers/tty/serial/qcom_geni_serial.c | 88 +++++++++++++++++++++-------------- 1 file changed, 53 insertions(+), 35 deletions(-)