linux-kernel - Re: [PATCH v3 11/11] serial: sc16is7xx: add dump registers function

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Message-ID: <2023052837-entree-broken-d7dd@gregkh>
Date:   Sun, 28 May 2023 12:56:31 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Hugo Villeneuve <hugo@...ovil.com>
Cc:     robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        conor+dt@...nel.org, jirislaby@...nel.org, jringle@...dpoint.com,
        tomasz.mon@...lingroup.com, l.perczak@...lintechnologies.com,
        linux-serial@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        Hugo Villeneuve <hvilleneuve@...onoff.com>
Subject: Re: [PATCH v3 11/11] serial: sc16is7xx: add dump registers function

On Thu, May 25, 2023 at 12:03:25AM -0400, Hugo Villeneuve wrote:
> From: Hugo Villeneuve <hvilleneuve@...onoff.com>
> 
> With this driver, it is very hard to debug the registers using
> the /sys/kernel/debug/regmap interface.
> 
> The main reason is that bits 0 and 1 of the register address
> correspond to the channels bits, so the register address itself starts
> at bit 2, so we must 'mentally' shift each register address by 2 bits
> to get its offset.
> 
> Also, only channels 0 and 1 are supported, so combinations of bits
> 0 and 1 being 10b and 11b are invalid, and the display of these
> registers is useless.
> 
> For example:
> 
> cat /sys/kernel/debug/regmap/spi0.0/registers
> 04: 10 -> Port 0, register offset 1
> 05: 10 -> Port 1, register offset 1
> 06: 00 -> Port 2, register offset 1 -> invalid
> 07: 00 -> port 3, register offset 1 -> invalid
> ...
> 
> Add a debug module parameter to call a custom dump function for each
> port registers after the probe phase to help debug.
> 
> Signed-off-by: Hugo Villeneuve <hvilleneuve@...onoff.com>
> ---
>  drivers/tty/serial/sc16is7xx.c | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
> 
> diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
> index 03d00b144304..693b6cc371f8 100644
> --- a/drivers/tty/serial/sc16is7xx.c
> +++ b/drivers/tty/serial/sc16is7xx.c
> @@ -347,6 +347,10 @@ struct sc16is7xx_port {
>  	struct sc16is7xx_one		p[];
>  };
>  
> +static bool debug;
> +module_param(debug, bool, 0644);
> +MODULE_PARM_DESC(debug, "enable/disable debug messages");

Sorry, but no, use the normal dynamic debugging logic that the whole
rest of the kernel uses.  Do not add random per-driver module parameters
like this, that would be a regression from the existing infrastructure
that we have in place already.

thanks,

greg k-h