linux-kernel - Re: [PATCH] serial: 8250: Add Nuvoton NPCM UART

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Date:   Thu, 15 Feb 2018 12:15:26 +0200
From:   Avi Fishman <avifishman70@...il.com>
To:     Joel Stanley <joel@....id.au>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-serial@...r.kernel.org,
        devicetree <devicetree@...r.kernel.org>,
        AP MS30 Linux Kernel community 
        <linux-kernel@...r.kernel.org>, Jeremy Kerr <jk@...abs.org>,
        Tomer Maimon <tmaimon77@...il.com>
Subject: Re: [PATCH] serial: 8250: Add Nuvoton NPCM UART

> From: joel.stan@...il.com [mailto:joel.stan@...il.com] On Behalf Of Joel Stanley
> Sent: Thursday, February 15, 2018 4:00 AM
>
> On Wed, Feb 14, 2018 at 3:22 AM, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
>> On Mon, Feb 12, 2018 at 6:48 AM, Joel Stanley <joel@....id.au> wrote:
>>> The Nuvoton UART is almost compatible with the 8250 driver when
>>> probed via the 8250_of driver, however it requires some extra
>>> configuration at startup.
>>
>>
>>> +       [PORT_NPCM] = {
>>> +               .name           = "Nuvoton 16550",
>>> +               .fifo_size      = 16,
>>> +               .tx_loadsz      = 16,
>>> +               .fcr            = UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_10 |
>>> +                                 UART_FCR_CLEAR_RCVR | UART_FCR_CLEAR_XMIT,
>>> +               .rxtrig_bytes   = {1, 4, 8, 14},
>>> +               .flags          = UART_CAP_FIFO,
>>
>>> +
>>
>> Redundant.
>
> You are referring to the extra whitespace?
>
>>> +       },
>>
>>> +               /*
>>> +                * Nuvoton calls the scratch register 'UART_TOR' (timeout
>>> +                * register). Enable it, and set TIOC (timeout interrupt
>>> +                * comparator) to be 0x20 for correct operation.
>>> +                */
>>> +               serial_port_out(port, UART_NPCM_TOR, UART_NPCM_TOIE |
>>> + 0x20);
>>
>>> +/* Nuvoton NPCM UARTs have a custom divisor calculation */
>>> +       return DIV_ROUND_CLOSEST(port->uartclk, 16 * baud + 2) - 2;
>>
>> Is there any link to datasheet?
>
> I have a copy of the datasheet under NDA. The Nuvoton guys might be able to help you out. Avi?

In the spec the calculation is as follows:
  BaudOut = Selected UART Clock Source / ( 16 * [Divisor + 2] )
To translate it to our code is:
  baud = port->uartclk / (16 * (Divisor + 2) )
So it should calculate without the "+ 2" inside as follow:
+       return DIV_ROUND_CLOSEST(port->uartclk, 16 * baud) - 2;

In order to get the spec you can add somthing like that:
"For getting the NPCM7XX Data Sheet please contact bmc_marketing@...oton.com".

BTW Andy, Intel has our Data Sheet under NDA, you can ask Mihm James
<james.mihm@...el.com>.

>
>>
>>> +/* Nuvoton UART */
>>> +#define PORT_NPCM      118
>>
>> We have gaps there. #40 is perfect place for this one.
>
> Ok, I will move it up. Thanks for the review.
>
> Cheers,
>
> Joel
>