linux-kernel - Re: [PATCH v2 10/13] tty: serial: atmel: Only divide Clock Divisor if the IP is USART

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Date:   Wed, 7 Sep 2022 09:34:54 +0000
From:   <Sergiu.Moga@...rochip.com>
To:     <ilpo.jarvinen@...ux.intel.com>
CC:     <lee@...nel.org>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <Nicolas.Ferre@...rochip.com>,
        <alexandre.belloni@...tlin.com>, <Claudiu.Beznea@...rochip.com>,
        <richard.genoud@...il.com>, <radu_nicolae.pirea@....ro>,
        <gregkh@...uxfoundation.org>, <broonie@...nel.org>,
        <mturquette@...libre.com>, <sboyd@...nel.org>,
        <jirislaby@...nel.org>, <admin@...iphile.com>,
        <Kavyasree.Kotagiri@...rochip.com>, <Tudor.Ambarus@...rochip.com>,
        <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-spi@...r.kernel.org>,
        <linux-serial@...r.kernel.org>, <linux-clk@...r.kernel.org>
Subject: Re: [PATCH v2 10/13] tty: serial: atmel: Only divide Clock Divisor if
 the IP is USART

On 07.09.2022 12:23, Ilpo Järvinen wrote:
> On Tue, 6 Sep 2022, Sergiu Moga wrote:
> 
>> Make sure that the driver only divides the clock divisor if the
>> IP handled at that point is USART, since UART IP's do not support
>> implicit peripheral clock division. Instead, in the case of UART,
>> go with the highest possible clock divisor.
>>
>> Signed-off-by: Sergiu Moga <sergiu.moga@...rochip.com>
>> ---
>>
>>
>> v1 -> v2:
>> - Nothing, this patch was not here before and is mainly meant as both cleanup
>> and as a way to introduce a new field into struct atmel_uart_port that will be
>> used by the last patch to diferentiate between USART and UART regarding the
>> location of the Baudrate Clock Source bitmask.
>>
>>
>>
>>
>>   drivers/tty/serial/atmel_serial.c | 13 ++++++++++++-
>>   1 file changed, 12 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
>> index 7450d3853031..6aa01ca5489c 100644
>> --- a/drivers/tty/serial/atmel_serial.c
>> +++ b/drivers/tty/serial/atmel_serial.c
>> @@ -150,6 +150,7 @@ struct atmel_uart_port {
>>        u32                     rts_low;
>>        bool                    ms_irq_enabled;
>>        u32                     rtor;   /* address of receiver timeout register if it exists */
>> +     bool                    is_usart;
>>        bool                    has_frac_baudrate;
>>        bool                    has_hw_timer;
>>        struct timer_list       uart_timer;
>> @@ -1825,6 +1826,7 @@ static void atmel_get_ip_name(struct uart_port *port)
>>         */
>>        atmel_port->has_frac_baudrate = false;
>>        atmel_port->has_hw_timer = false;
>> +     atmel_port->is_usart = false;
>>
>>        if (name == new_uart) {
>>                dev_dbg(port->dev, "Uart with hw timer");
>> @@ -1834,6 +1836,7 @@ static void atmel_get_ip_name(struct uart_port *port)
>>                dev_dbg(port->dev, "Usart\n");
>>                atmel_port->has_frac_baudrate = true;
>>                atmel_port->has_hw_timer = true;
>> +             atmel_port->is_usart = true;
>>                atmel_port->rtor = ATMEL_US_RTOR;
>>                version = atmel_uart_readl(port, ATMEL_US_VERSION);
>>                switch (version) {
>> @@ -1863,6 +1866,7 @@ static void atmel_get_ip_name(struct uart_port *port)
>>                        dev_dbg(port->dev, "This version is usart\n");
>>                        atmel_port->has_frac_baudrate = true;
>>                        atmel_port->has_hw_timer = true;
>> +                     atmel_port->is_usart = true;
>>                        atmel_port->rtor = ATMEL_US_RTOR;
>>                        break;
>>                case 0x203:
>> @@ -2282,10 +2286,17 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
>>                cd = uart_get_divisor(port, baud);
>>        }
>>
>> -     if (cd > 65535) {       /* BRGR is 16-bit, so switch to slower clock */
>> +     /*
>> +      * BRGR is 16-bit, so switch to slower clock.
>> +      * Otherwise, keep the highest possible value for the clock divisor.
>> +      */
>> +     if (atmel_port->is_usart && cd > 65535) {
> 
> Should this be cd > ATMEL_US_CD ?
> 
>>                cd /= 8;
>>                mode |= ATMEL_US_USCLKS_MCK_DIV8;
>> +     } else {
>> +             cd &= 65535;
> 
> ATMEL_US_CD?


Yes, it would seem that would be right. It did not cross my mind to 
check whether there already was something pre-defined or not since the 
code also previously used 65535.

> 
>>        }
>> +
>>        quot = cd | fp << ATMEL_US_FP_OFFSET;
>>
>>        if (!(port->iso7816.flags & SER_ISO7816_ENABLED))
>>
> 
> --
>   i.
> 


Thanks,
	Sergiu