linux-kernel - Re: [PATCH v2 2/2] serial: 8250: Add new 8250-core based Broadcom STB driver

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Message-ID: <YAXJRDhS1HXeYaZz@kroah.com>
Date:   Mon, 18 Jan 2021 18:45:40 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Al Cooper <alcooperx@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com, devicetree@...r.kernel.org,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-serial@...r.kernel.org, linux-usb@...r.kernel.org,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH v2 2/2] serial: 8250: Add new 8250-core based Broadcom
 STB driver

On Fri, Jan 15, 2021 at 04:15:43PM -0500, Al Cooper wrote:
> Add a UART driver for the new Broadcom 8250 based STB UART. The new
> UART is backward compatible with the standard 8250, but has some
> additional features. The new features include a high accuracy baud
> rate clock system and DMA support.
> 
> The driver will use the new optional BAUD MUX clock to select the best
> one of the four master clocks (81MHz, 108MHz, 64MHz and 48MHz) to feed
> the baud rate selection logic for any requested baud rate.  This allows
> for more accurate BAUD rates when high speed baud rates are selected.
> 
> The driver will use the new UART DMA hardware if the UART DMA registers
> are specified in Device Tree "reg" property. The DMA functionality can
> be disabled on kernel boot with the argument:
> "8250_bcm7271.disable_dma=Y".

Shouldn't that be on a per-device basis, and not a per-driver basis?

And why would you want to disable this, if you have support for this in
the DT?  Why not just rely on the DT setting?

thanks,

greg k-h