Re: [PATCH 1/7] serial: 8250_dma: Use ->tx_dma function pointer to start next DMA

From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: linux-renesas-soc@vger.kernel.org,
	Magnus Damm <magnus.damm@gmail.com>,
	Gareth Williams <gareth.williams.jx@renesas.com>,
	Phil Edworthy <phil.edworthy@renesas.com>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jirislaby@kernel.org>,
	linux-serial@vger.kernel.org,
	Milan Stevanovic <milan.stevanovic@se.com>,
	Jimmy Lalande <jimmy.lalande@se.com>,
	Pascal Eberhard <pascal.eberhard@se.com>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	Herve Codina <herve.codina@bootlin.com>,
	Clement Leger <clement.leger@bootlin.com>
Subject: Re: [PATCH 1/7] serial: 8250_dma: Use ->tx_dma function pointer to start next DMA
Date: Thu, 10 Mar 2022 19:59:17 +0200	[thread overview]
Message-ID: <Yio8dcOPPyCWbBMa@smile.fi.intel.com> (raw)
In-Reply-To: <20220310161650.289387-2-miquel.raynal@bootlin.com>

On Thu, Mar 10, 2022 at 05:16:44PM +0100, Miquel Raynal wrote:
> From: Phil Edworthy <phil.edworthy@renesas.com>
> 
> The 8250 driver is quite flexible. Regarding DMA handling, there is the
> possibility to either use the default helper (serial8250_tx_dma()) or
> call a specific function. Only the omap and brcm implementation do
> that. In both cases, they don't use the serial8250_tx_dma() helper at
> all.
> 
> As we are going to write a new DMA handling function for the RZ/N1 SoCs
> which will use the serial8250_tx_dma() implementation (preceded by a
> couple of register writes), we need the ->tx_dma() pointer to link to
> our own function, but within the __dma_tx_complete() helper we also need
> to call our own implementation instead of the default one directly.
> 
> In order to do that, let's call ->tx_dma() instead of
> serial8250_tx_dma() from __dma_tx_complete().

In 8250 driver the pattern is to give the generic function "do" name and
then call it in a wrapper:

	if (->foo())
		return ->foo();

	return serial8250_do_foo();

There are plenty of examples in that driver.

-- 
With Best Regards,
Andy Shevchenko