linux-kernel - Re: [PATCH 1/1] xilinx ps uart: Adding a kernel parameter for the number of xilinx ps uarts

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Date:   Mon, 22 May 2017 19:26:36 +0100
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     Michal Simek <michal.simek@...inx.com>
Cc:     Sam Povilus <kernel.development@...il.us>,
        <gregkh@...uxfoundation.org>, <jslaby@...e.com>,
        <soren.brinkmann@...inx.com>, <linux-serial@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] xilinx ps uart: Adding a kernel parameter for the
 number of xilinx ps uarts

> We have in soc vendor tree similar patch but the reason is different.
> 
>     tty: serial: Added a CONFIG_SERIAL_XILINX_NR_UARTS option.
> 
>     This patch Adds CONFIG_SERIAL_XILINX_NR_UARTS option to allow
>     the user to provide the Max number of uart ports information.
>     If multiple cards (or) PL UARTS are present, the default limit
>     of 2 ports should be increased.
> 
> I haven't checked all drivers but in our case we have added this as
> quick fix for scenarios where you use serial aliases where alias is
> pointed to serial2 or more.
> In cdns_uart_init() cdns_uart_uart_driver is passed which contains .nr
> which is required to be passed.
> 
> What's the best driver to look at dynamic allocation?

So there are quite a few that dynamically allocate the objects as they
are enumerated (eg max3100), but have a maximum set that is just pointers
(so for the max number of ports cheaper than the dynamic code)

The other question is why is it a CONFIG_ option. I'm assuming these
platforms are all ARM and in that case you could just pass the value in
the device tree, or hard code a safe maximum number of pointers to a
value which is the worst case and then install them as they are
enumerated.

There are lots of options better than breaking the "one kernel many
platforms" model.

Alan