| Message ID | 1652697510-30543-1-git-send-email-quic_vnivarth@quicinc.com |
|---|---|
| State | New |
| Headers | show |
| Series | [V2] tty: serial: qcom-geni-serial: Remove uart frequency table. Instead, find suitable frequency with call to clk_round_rate. | expand |
Hi, On Mon, May 16, 2022 at 3:38 AM Vijaya Krishna Nivarthi <quic_vnivarth@quicinc.com> wrote: > > Replace the UART frequency table 'root_freq[]' with logic around > clk_round_rate() so that SoC details like the available clk frequencies > can change and this driver still works. This reduces tight coupling > between this UART driver and the SoC clk driver because we no longer > have to update the 'root_freq[]' array for new SoCs. Instead the driver > determines the available frequencies at runtime. > > Signed-off-by: Vijaya Krishna Nivarthi <quic_vnivarth@quicinc.com> > --- > v2: loops through clk dividers to zero-in quickly > v1: intial patch looped through available clk frequencies > --- > drivers/tty/serial/qcom_geni_serial.c | 56 ++++++++++++++++++++++------------- > 1 file changed, 36 insertions(+), 20 deletions(-) > > diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c > index f496102..4733a23 100644 > --- a/drivers/tty/serial/qcom_geni_serial.c > +++ b/drivers/tty/serial/qcom_geni_serial.c > @@ -149,12 +149,6 @@ static unsigned int qcom_geni_serial_tx_empty(struct uart_port *port); > static void qcom_geni_serial_stop_rx(struct uart_port *uport); > static void qcom_geni_serial_handle_rx(struct uart_port *uport, bool drop); > > -static const unsigned long root_freq[] = {7372800, 14745600, 19200000, 29491200, > - 32000000, 48000000, 51200000, 64000000, > - 80000000, 96000000, 100000000, > - 102400000, 112000000, 120000000, > - 128000000}; > - > #define to_dev_port(ptr, member) \ > container_of(ptr, struct qcom_geni_serial_port, member) > > @@ -946,25 +940,43 @@ static int qcom_geni_serial_startup(struct uart_port *uport) > return 0; > } > > -static unsigned long get_clk_cfg(unsigned long clk_freq) > -{ > - int i; > - > - for (i = 0; i < ARRAY_SIZE(root_freq); i++) { > - if (!(root_freq[i] % clk_freq)) > - return root_freq[i]; > - } > - return 0; > -} > - > -static unsigned long get_clk_div_rate(unsigned int baud, > +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; > + unsigned long freq, prev; > + unsigned long div, maxdiv; > + int64_t mult; Why is "mult" signed? Shouldn't it be type "u64" or something? > > desired_clk = baud * sampling_rate; > - ser_clk = get_clk_cfg(desired_clk); > + if (!desired_clk) { > + pr_err("%s: Invalid frequency\n", __func__); nit: IMO printing the __func__ in every printout is not a good practice. It uglifies the kernel log buffer. If you personally truly want the function in every printout then modify pr_err() to print it. > + return 0; > + } > + > + maxdiv = CLK_DIV_MSK >> CLK_DIV_SHFT; > + prev = 0; > + > + for (div = 1; div <= maxdiv; div++) { > + mult = div * desired_clk; > + if (mult > ULONG_MAX) > + break; I'm pretty sure your "if" test is always false because you didn't cast properly. I even tested it for you: { unsigned long a, b; unsigned long long c; printf("long size: %d, long long size: %d\n", (int)(sizeof(a)), (int)(sizeof(c))); a = 0xffffffff; b = 2; c = a * b; printf("c is %#llx\n", c); c = a * (unsigned long long)b; printf("c is %#llx\n", c); } That prints out: long size: 4, long long size: 8 c is 0xfffffffe c is 0x1fffffffe > + > + freq = clk_round_rate(clk, (unsigned long)mult); > + if (!(freq % desired_clk)) { > + ser_clk = freq; > + break; > + } > + > + if (!prev) > + ser_clk = freq; Instead of the above, why not just init ser_clk to "desired_clk"? ...or perhaps leave it initted to 0 so your error check after the loop isn't dead code? > + else if (prev == freq) > + break; Are you sure about this exit condition? It seems wrong. I guess you're assuming that clk_round_rate() will round up like it (almost always) does for the Qualcomm clock driver. So I guess let's say we're trying to make 10000 baud and your oversampling is 16. So "desired_clk" is 160000, right? Now let's imagine that the clock driver can make three rates: 7372800, 14745600, 19200000 Your loop will run. The first time through we'll "round" 160000 and get back 7372800. It's not a match. Prev will now be 7372800. The second time through, we'll round (160000 * 2) and get back 7372800. It's not a match and prev will be equal to freq so we'll break. ...but we _should_ have found 19200000 So I think this break condition is wrong. > + > + prev = freq; > + } > + > if (!ser_clk) { > pr_err("%s: Can't find matching DFS entry for baud %d\n", > __func__, baud); In the above, you _always_ init "ser_clk" to something, so how can this error condition ever occur in your new code? > @@ -972,6 +984,9 @@ static unsigned long get_clk_div_rate(unsigned int baud, > } > > *clk_div = ser_clk / desired_clk; > + if (!(*clk_div)) > + *clk_div = 1; I _think_ this can be removed if you just don't allow inexact matches. ...if you do allow inexact matches, maybe you should put a warning in the logs in that case? > + > return ser_clk; > } > > @@ -1003,7 +1018,8 @@ 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(baud, sampling_rate, &clk_div); > + clk_rate = get_clk_div_rate(port->se.clk, baud, > + sampling_rate, &clk_div); IMO it would look better to just let the above line be 81 columns rather than the ugly wrapping.
Thanks a lot for very useful feedback. I see that the patch has landed, will upload another incorporating these suggestions. -Vijay/ -----Original Message----- From: Doug Anderson <dianders@chromium.org> Sent: Thursday, May 26, 2022 10:38 PM To: Vijaya Krishna Nivarthi (Temp) (QUIC) <quic_vnivarth@quicinc.com> Cc: Andy Gross <agross@kernel.org>; bjorn.andersson@linaro.org; Greg Kroah-Hartman <gregkh@linuxfoundation.org>; Jiri Slaby <jirislaby@kernel.org>; linux-arm-msm <linux-arm-msm@vger.kernel.org>; linux-serial@vger.kernel.org; LKML <linux-kernel@vger.kernel.org>; Mukesh Savaliya (QUIC) <quic_msavaliy@quicinc.com>; Matthias Kaehlcke <mka@chromium.org>; Stephen Boyd <swboyd@chromium.org>; Satya Priya Kakitapalli (Temp) (QUIC) <quic_c_skakit@quicinc.com> Subject: Re: [V2] tty: serial: qcom-geni-serial: Remove uart frequency table. Instead, find suitable frequency with call to clk_round_rate. WARNING: This email originated from outside of Qualcomm. Please be wary of any links or attachments, and do not enable macros. Hi, On Mon, May 16, 2022 at 3:38 AM Vijaya Krishna Nivarthi <quic_vnivarth@quicinc.com> wrote: > > Replace the UART frequency table 'root_freq[]' with logic around > clk_round_rate() so that SoC details like the available clk > frequencies can change and this driver still works. This reduces tight > coupling between this UART driver and the SoC clk driver because we no > longer have to update the 'root_freq[]' array for new SoCs. Instead > the driver determines the available frequencies at runtime. > > Signed-off-by: Vijaya Krishna Nivarthi <quic_vnivarth@quicinc.com> > --- > v2: loops through clk dividers to zero-in quickly > v1: intial patch looped through available clk frequencies > --- > drivers/tty/serial/qcom_geni_serial.c | 56 > ++++++++++++++++++++++------------- > 1 file changed, 36 insertions(+), 20 deletions(-) > > diff --git a/drivers/tty/serial/qcom_geni_serial.c > b/drivers/tty/serial/qcom_geni_serial.c > index f496102..4733a23 100644 > --- a/drivers/tty/serial/qcom_geni_serial.c > +++ b/drivers/tty/serial/qcom_geni_serial.c > @@ -149,12 +149,6 @@ static unsigned int > qcom_geni_serial_tx_empty(struct uart_port *port); static void > qcom_geni_serial_stop_rx(struct uart_port *uport); static void > qcom_geni_serial_handle_rx(struct uart_port *uport, bool drop); > > -static const unsigned long root_freq[] = {7372800, 14745600, 19200000, 29491200, > - 32000000, 48000000, 51200000, 64000000, > - 80000000, 96000000, 100000000, > - 102400000, 112000000, 120000000, > - 128000000}; > - > #define to_dev_port(ptr, member) \ > container_of(ptr, struct qcom_geni_serial_port, > member) > > @@ -946,25 +940,43 @@ static int qcom_geni_serial_startup(struct uart_port *uport) > return 0; > } > > -static unsigned long get_clk_cfg(unsigned long clk_freq) -{ > - int i; > - > - for (i = 0; i < ARRAY_SIZE(root_freq); i++) { > - if (!(root_freq[i] % clk_freq)) > - return root_freq[i]; > - } > - return 0; > -} > - > -static unsigned long get_clk_div_rate(unsigned int baud, > +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; > + unsigned long freq, prev; > + unsigned long div, maxdiv; > + int64_t mult; Why is "mult" signed? Shouldn't it be type "u64" or something?
diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c index f496102..4733a23 100644 --- a/drivers/tty/serial/qcom_geni_serial.c +++ b/drivers/tty/serial/qcom_geni_serial.c @@ -149,12 +149,6 @@ static unsigned int qcom_geni_serial_tx_empty(struct uart_port *port); static void qcom_geni_serial_stop_rx(struct uart_port *uport); static void qcom_geni_serial_handle_rx(struct uart_port *uport, bool drop); -static const unsigned long root_freq[] = {7372800, 14745600, 19200000, 29491200, - 32000000, 48000000, 51200000, 64000000, - 80000000, 96000000, 100000000, - 102400000, 112000000, 120000000, - 128000000}; - #define to_dev_port(ptr, member) \ container_of(ptr, struct qcom_geni_serial_port, member) @@ -946,25 +940,43 @@ static int qcom_geni_serial_startup(struct uart_port *uport) return 0; } -static unsigned long get_clk_cfg(unsigned long clk_freq) -{ - int i; - - for (i = 0; i < ARRAY_SIZE(root_freq); i++) { - if (!(root_freq[i] % clk_freq)) - return root_freq[i]; - } - return 0; -} - -static unsigned long get_clk_div_rate(unsigned int baud, +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; + unsigned long freq, prev; + unsigned long div, maxdiv; + int64_t mult; desired_clk = baud * sampling_rate; - ser_clk = get_clk_cfg(desired_clk); + if (!desired_clk) { + pr_err("%s: Invalid frequency\n", __func__); + return 0; + } + + maxdiv = CLK_DIV_MSK >> CLK_DIV_SHFT; + prev = 0; + + for (div = 1; div <= maxdiv; div++) { + mult = div * desired_clk; + if (mult > ULONG_MAX) + break; + + freq = clk_round_rate(clk, (unsigned long)mult); + if (!(freq % desired_clk)) { + ser_clk = freq; + break; + } + + if (!prev) + ser_clk = freq; + else if (prev == freq) + break; + + prev = freq; + } + if (!ser_clk) { pr_err("%s: Can't find matching DFS entry for baud %d\n", __func__, baud); @@ -972,6 +984,9 @@ static unsigned long get_clk_div_rate(unsigned int baud, } *clk_div = ser_clk / desired_clk; + if (!(*clk_div)) + *clk_div = 1; + return ser_clk; } @@ -1003,7 +1018,8 @@ 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(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;
Replace the UART frequency table 'root_freq[]' with logic around clk_round_rate() so that SoC details like the available clk frequencies can change and this driver still works. This reduces tight coupling between this UART driver and the SoC clk driver because we no longer have to update the 'root_freq[]' array for new SoCs. Instead the driver determines the available frequencies at runtime. Signed-off-by: Vijaya Krishna Nivarthi <quic_vnivarth@quicinc.com> --- v2: loops through clk dividers to zero-in quickly v1: intial patch looped through available clk frequencies --- drivers/tty/serial/qcom_geni_serial.c | 56 ++++++++++++++++++++++------------- 1 file changed, 36 insertions(+), 20 deletions(-)