linux-kernel - Re: [PATCH v2 1/3] tty: Introduce UART_CAP

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Date:	Sat, 7 Nov 2015 17:04:43 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	"Matwey V. Kornilov" <matwey@....msu.ru>
Cc:	Greg KH <gregkh@...uxfoundation.org>, jslaby@...e.com,
	linux-serial@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] tty: Introduce UART_CAP_HW485

On 11/07/2015 04:10 PM, Matwey V. Kornilov wrote:
> 2015-11-07 18:32 GMT+03:00 Peter Hurley <peter@...leysoftware.com>:
>> On 11/07/2015 07:39 AM, Matwey V. Kornilov wrote:
>>> 2015-11-07 15:22 GMT+03:00 Peter Hurley <peter@...leysoftware.com>:
>>>> On 11/07/2015 05:09 AM, Matwey V. Kornilov wrote:
>>>>> Introduce new capability UART_CAP_HW485 to mark 8250 UARTs which have
>>>>> hardware support of line direction control.
>>>>
>>>> Since capabilities are not exported to user-space, how will user-space
>>>> know if the port only provides emulated 485 (eg., where only HW485 is
>>>> acceptable)?
>>>
>>> I cannot imagine the case when user really has to care about
>>> implementation details.
>>> In both cases the user will be provided with the consistent API
>>> (TIOCGRS485/TIOCSRS485 ioctls) resulting into the same behavior.
>>> Could you please expand your question?
>>
>> Well, the entire serial core is a 'consistent' API but yet we
>> still report to user-space what the port type is. Same with lspci
>> and lsusb.
> 
> Yes, that is correct.
> I mean if you want the knowledge about HW485 be provided to the
> user-space via some ioctl, then I cannot understand what application
> is going to do with it.
> It has single one option: use provided RS485 if it needs RS485, it
> cannot purchase and install other hardware in runtime.
> But I think we could add new read-only flag to struct serial_rs485,
> say SER_RS485_SOFTWARE then user will know that software emulation is
> being used.
> Would it be ok?

Yes, something like that would be fine.

Regards,
Peter Hurley


>>>>> Signed-off-by: Matwey V. Kornilov <matwey@....msu.ru>
>>>>> ---
>>>>> Changes since v1:
>>>>>  - Commit message has been wrapped
>>>>>
>>>>>  drivers/tty/serial/8250/8250.h         | 1 +
>>>>>  drivers/tty/serial/8250/8250_fintek.c  | 1 +
>>>>>  drivers/tty/serial/8250/8250_lpc18xx.c | 1 +
>>>>>  drivers/tty/serial/8250/8250_pci.c     | 1 +
>>>>>  4 files changed, 4 insertions(+)
>>>>>
>>>>> diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
>>>>> index d54dcd8..92a4f47 100644
>>>>> --- a/drivers/tty/serial/8250/8250.h
>>>>> +++ b/drivers/tty/serial/8250/8250.h
>>>>> @@ -69,6 +69,7 @@ struct serial8250_config {
>>>>>       unsigned int    flags;
>>>>>  };
>>>>>
>>>>> +#define UART_CAP_HW485       (1 << 7)        /* UART has hardware direction control for RS485 */
>>>>>  #define UART_CAP_FIFO        (1 << 8)        /* UART has FIFO */
>>>>>  #define UART_CAP_EFR (1 << 9)        /* UART has EFR */
>>>>>  #define UART_CAP_SLEEP       (1 << 10)       /* UART has IER sleep */
>>>>> diff --git a/drivers/tty/serial/8250/8250_fintek.c b/drivers/tty/serial/8250/8250_fintek.c
>>>>> index 8947439..f2831a8 100644
>>>>> --- a/drivers/tty/serial/8250/8250_fintek.c
>>>>> +++ b/drivers/tty/serial/8250/8250_fintek.c
>>>>> @@ -208,6 +208,7 @@ fintek_8250_probe(struct pnp_dev *dev, const struct pnp_device_id *dev_id)
>>>>>       uart.port.iobase = pnp_port_start(dev, 0);
>>>>>       uart.port.iotype = UPIO_PORT;
>>>>>       uart.port.rs485_config = fintek_8250_rs485_config;
>>>>> +     uart.capabilities = UART_CAP_HW485;
>>>>>
>>>>>       uart.port.flags |= UPF_SKIP_TEST | UPF_BOOT_AUTOCONF;
>>>>>       if (pnp_irq_flags(dev, 0) & IORESOURCE_IRQ_SHAREABLE)
>>>>> diff --git a/drivers/tty/serial/8250/8250_lpc18xx.c b/drivers/tty/serial/8250/8250_lpc18xx.c
>>>>> index 99cd478..9d30276 100644
>>>>> --- a/drivers/tty/serial/8250/8250_lpc18xx.c
>>>>> +++ b/drivers/tty/serial/8250/8250_lpc18xx.c
>>>>> @@ -175,6 +175,7 @@ static int lpc18xx_serial_probe(struct platform_device *pdev)
>>>>>       uart.port.private_data = data;
>>>>>       uart.port.rs485_config = lpc18xx_rs485_config;
>>>>>       uart.port.serial_out = lpc18xx_uart_serial_out;
>>>>> +     uart.capabilities = UART_CAP_HW485;
>>>>>
>>>>>       uart.dma = &data->dma;
>>>>>       uart.dma->rxconf.src_maxburst = 1;
>>>>> diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c
>>>>> index 4097f3f..c7c0ae9 100644
>>>>> --- a/drivers/tty/serial/8250/8250_pci.c
>>>>> +++ b/drivers/tty/serial/8250/8250_pci.c
>>>>> @@ -1599,6 +1599,7 @@ static int pci_fintek_setup(struct serial_private *priv,
>>>>>       port->port.iotype = UPIO_PORT;
>>>>>       port->port.iobase = iobase;
>>>>>       port->port.rs485_config = pci_fintek_rs485_config;
>>>>> +     port->capabilities = UART_CAP_HW485;
>>>>>
>>>>>       data = devm_kzalloc(&pdev->dev, sizeof(u8), GFP_KERNEL);
>>>>>       if (!data)

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