linux-kernel - Re: [PATCH 5.10 044/390] serial: 8250: Let drivers request full 16550A feature probing

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Date:   Mon, 24 Oct 2022 19:27:10 +0200
From:   Pavel Machek <pavel@....cz>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Anders Blomdell <anders.blomdell@...trol.lth.se>,
        "Maciej W. Rozycki" <macro@...am.me.uk>
Subject: Re: [PATCH 5.10 044/390] serial: 8250: Let drivers request full
 16550A feature probing

Hi!

> From: Maciej W. Rozycki <macro@...am.me.uk>
> 
> commit 9906890c89e4dbd900ed87ad3040080339a7f411 upstream.
> 
> A SERIAL_8250_16550A_VARIANTS configuration option has been recently
> defined that lets one request the 8250 driver not to probe for 16550A
> device features so as to reduce the driver's device startup time in
> virtual machines.
> 
> Some actual hardware devices require these features to have been fully
> determined however for their driver to work correctly, so define a flag
> to let drivers request full 16550A feature probing on a device-by-device
> basis if required regardless of the SERIAL_8250_16550A_VARIANTS option
> setting chosen.

As far as I can see, the UPF_FULL_PROBE is never set in 5.10.150 tree,
so we should not need it there.

Best regards,
								Pavel

> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -1021,7 +1021,8 @@ static void autoconfig_16550a(struct uar
>  	up->port.type = PORT_16550A;
>  	up->capabilities |= UART_CAP_FIFO;
>  
> -	if (!IS_ENABLED(CONFIG_SERIAL_8250_16550A_VARIANTS))
> +	if (!IS_ENABLED(CONFIG_SERIAL_8250_16550A_VARIANTS) &&
> +	    !(up->port.flags & UPF_FULL_PROBE))
>  		return;
>  
>  	/*
> --- a/include/linux/serial_core.h
> +++ b/include/linux/serial_core.h
> @@ -100,7 +100,7 @@ struct uart_icount {
>  	__u32	buf_overrun;
>  };
>  
> -typedef unsigned int __bitwise upf_t;
> +typedef u64 __bitwise upf_t;
>  typedef unsigned int __bitwise upstat_t;
>  
>  struct uart_port {
> @@ -207,6 +207,7 @@ struct uart_port {
>  #define UPF_FIXED_PORT		((__force upf_t) (1 << 29))
>  #define UPF_DEAD		((__force upf_t) (1 << 30))
>  #define UPF_IOREMAP		((__force upf_t) (1 << 31))
> +#define UPF_FULL_PROBE		((__force upf_t) (1ULL << 32))
>  
>  #define __UPF_CHANGE_MASK	0x17fff
>  #define UPF_CHANGE_MASK		((__force upf_t) __UPF_CHANGE_MASK)
> 

-- 
People of Russia, stop Putin before his war on Ukraine escalates.

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