[PATCH v5 5/5] tty/serial: Add Spreadtrum sc9836-uart driver support

[Lyra Zhang]

Hi, Rob

I still have a question to be conform, specific describes below:

On Mon, Jan 19, 2015 at 10:11 PM, Rob Herring <robherring2 at gmail.com> wrote:
> On Mon, Jan 19, 2015 at 3:55 AM, Lyra Zhang <zhang.lyra at gmail.com> wrote:
>> On Sat, Jan 17, 2015 at 12:41 AM, Rob Herring <robherring2 at gmail.com> wrote:
>>> On Fri, Jan 16, 2015 at 4:00 AM, Chunyan Zhang
>>> <chunyan.zhang at spreadtrum.com> wrote:
>>>> Add a full sc9836-uart driver for SC9836 SoC which is based on the
>>>> spreadtrum sharkl64 platform.
>>>> This driver also support earlycon.
>>>> This patch also replaced the spaces between the macros and their
>>>> values with the tabs in serial_core.h
>
> [...]
>
>>>> +static int __init sprd_serial_init(void)
>>>> +{
>>>> +       int ret = 0;
>>>> +
>>>> +       ret = uart_register_driver(&sprd_uart_driver);
>>>
>>> This can be done in probe now. Then you can use module_platform_driver().
>>>
>>
>> Question:
>> 1. there are 4 uart ports configured in dt for sprd_serial, so probe
>> will be called 4 times, but uart_register_driver only needs to be
>> called one time, so can we use uart_driver.state to check if
>> uart_register_driver has already been called ?
>
> Yes.
>
>> 2. if I use module_platform_driver() instead of
>> module_init(sprd_serial_init)  and  module_exit(sprd_serial_exit) , I
>> must move uart_unregister_driver() which is now processed in
>> sprd_serial_exit() to sprd_remove(), there is a similar problem with
>> probe(), sprd_remove() will also be called 4 times, and actually it
>> should be called only one time. How can we deal with this case?
>
> Look at pl01x or Samsung UART drivers which have done this conversion.

Samsung UART does use module_platform_driver, but pl010/pl011 doesn't.
In the Samsung UART driver, uart_unregister_driver is processed in
remove(), like below:

static int s3c24xx_serial_remove(struct platform_device *dev)
{
    struct uart_port *port = s3c24xx_dev_to_port(&dev->dev);

    if (port) {
        s3c24xx_serial_cpufreq_deregister(to_ourport(port));
        uart_remove_one_port(&s3c24xx_uart_drv, port);
    }

    uart_unregister_driver(&s3c24xx_uart_drv);
}

if this serial has more than one ports, uart_unregister_driver() must
be called multiple times when the device need to be removed.
I think there may be a problem because that uart_unregister_driver()
will do kfree(drv->state) every time when it's called.

Thanks,
Chunyan

>
>> 3. for the second question, we can check the platform_device->id, if
>> it is equal to the index of last port (e.g. 4 for this case), then
>> uart_unregister_driver() can be called. Does it work correctly? since
>> for this case, we must keep the order of releasing ports.
>
> The id will not be the line index in the DT case. I don't think you
> can guarantee the order either.
>
> It would be better to make uart_{un}register_driver deal with being
> called multiple times so drivers don't have to deal with getting this
> correct. I'm not sure if that is feasible though.
>
> Rob