Re: [PATCH 05/18] tty: serial: samsung_tty: add support for Apple UARTs

On Tue, Feb 09, 2021 at 01:10:02AM +0900, Hector Martin wrote:

On 08/02/2021 19.54, Krzysztof Kozlowski wrote:

quoted

quoted

+enum s3c24xx_irq_type {
+	IRQ_DISCRETE = 0,
+	IRQ_S3C6400 = 1,
+	IRQ_APPLE = 2,

It seems you add the third structure to differentiate type of UART.
There is already port type and s3c24xx_serial_drv_data, no need for
third structure (kind of similar to tries of Tamseel Shams in recent
patches). It's too much. Instead, differentiate by port type or prepare
own set of uart_ops if it's really different (like you did with startup
op).

This ties into little changes in a bunch of places, so separate uart_ops
callbacks for every one of those would end up duplicating a lot of code :(

That list is just used to map the port type to something that only
represents the type of IRQs, but its only real purpose for the indirection
is so I can do "== IRQ_DISCRETE" in some codepaths to mean "not apple or
S3C6400".

e.g.

    if (s3c24xx_irq_type(port) == IRQ_DISCRETE)
        free_irq(ourport->rx_irq, ourport);

Would have to become

    if (port->type != IRQ_S3C6400 && port->type != IRQ_APPLE)
        free_irq(ourport->rx_irq, ourport);

or

    switch (port->type) {
    case IRQ_S3C6400:
    case IRQ_APPLE:
        break;
    default:
        free_irq(ourport->rx_irq, ourport);
    }

Which one do you prefer?

The latter, especially that switches will appear quite a lot in such
case.

However this pattern (== IRQ_DISCRETE) appears only in three places so
it should not be the main case considered here.

However I saw later you actually replaced the
s3c24xx_serial_has_interrupt_mask(), so it's not that bad.

In most of your code, there will be actually a switch with all three
cases.

Aside: Marc didn't like introducing new port types into uapi, but if we
don't do that then we need a "real" port type in drv_data that isn't the
uapi-exposed port or something along those lines, with a separate enum
containing all the true port type values for that.

Looking at Greg's comment, we can get rid of the PORT_ stuff entirely.
First of all, PORT_S3C2410 == PORT_S3C2412, so this define is not
accurate.

This leaves us with three types (s3c2400, s3c2440, s3c6410 and Apple).
The s3c2440 could be removed with adding a new "ucon_mask" field to
s3c24xx_serial_drv_data.

This would end with s3c24xx, s3c6410 and Apple - quite nice choice.

quoted

quoted

  	/* Startup sequence is different for s3c64xx and higher SoC's */
-	if (s3c24xx_serial_has_interrupt_mask(port))
+	case IRQ_S3C6400:
  		s3c24xx_serial_ops.startup = s3c64xx_serial_startup;

Don't overwrite specific ops. It's difficult to see then which ops are
being used. Instead create a new set of uart_ops matching the needs.

s3c24xx_serial_ops was already doing that here, but I can move that to a a
separate uart_ops too.

You're right. This one would have to be improved before your change.
Instead of replacing specific op calls in startup, I think it's better
to have entirely separate ops instance for each variant:

static const struct uart_ops s3c24xx_serial_ops;
static const struct uart_ops s3c64xx_serial_ops;
static const struct uart_ops s5l_serial_ops;

This allows to add a "const", since uart_port takes such const pointer.

Still during s3c24xx_serial_probe() correct ops would have to be
assigned, but at least all ops are easily visible.

Best regards,
Krzysztof