On Tue, Dec 19, 2023 at 12:19:01PM -0500, Hugo Villeneuve wrote:
> From: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
>
> Move common code for EFR lock/unlock of mutex into functions for code reuse
> and clarity.
...
> @@ -333,6 +333,7 @@ struct sc16is7xx_one {
> struct sc16is7xx_one_config config;
> bool irda_mode;
> unsigned int old_mctrl;
> + u8 old_lcr; /* Value before EFR access. */
> };
Have you run `pahole`?
I believe with
unsigned int old_mctrl;
u8 old_lcr; /* Value before EFR access. */
bool irda_mode;
layout it will take less memory.
...
> +/* In an amazing feat of design, the Enhanced Features Register (EFR)
/*
* This is NOT the style we use for multi-line
* comments in the serial subsystem. On contrary
* this comment can be used as a proper example.
* (Yes, I noticed it's an old comment, but take
* a chance to fix it.)
*/
> + * shares the address of the Interrupt Identification Register (IIR).
> + * Access to EFR is switched on by writing a magic value (0xbf) to the
> + * Line Control Register (LCR). Any interrupt firing during this time will
> + * see the EFR where it expects the IIR to be, leading to
> + * "Unexpected interrupt" messages.
> + *
> + * Prevent this possibility by claiming a mutex while accessing the EFR,
> + * and claiming the same mutex from within the interrupt handler. This is
> + * similar to disabling the interrupt, but that doesn't work because the
> + * bulk of the interrupt processing is run as a workqueue job in thread
> + * context.
> + */
...
> + sc16is7xx_port_write(port, SC16IS7XX_LCR_REG,
> + SC16IS7XX_LCR_CONF_MODE_B);
One line. (Yes, 81 character, but readability is as good as before.
--
With Best Regards,
Andy Shevchenko
