Re: [PATCH v3 0/4] tty: TX helpers

From: Jiri Slaby <jirislaby@kernel.org>
To: Johan Hovold <johan@kernel.org>
Cc: gregkh@linuxfoundation.org,
	"Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>,
	linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org,
	"Tobias Klauser" <tklauser@distanz.ch>,
	"Richard Genoud" <richard.genoud@gmail.com>,
	"Nicolas Ferre" <nicolas.ferre@microchip.com>,
	"Alexandre Belloni" <alexandre.belloni@bootlin.com>,
	"Claudiu Beznea" <claudiu.beznea@microchip.com>,
	"Vladimir Zapolskiy" <vz@mleia.com>,
	"Liviu Dudau" <liviu.dudau@arm.com>,
	"Sudeep Holla" <sudeep.holla@arm.com>,
	"Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
	"Shawn Guo" <shawnguo@kernel.org>,
	"Sascha Hauer" <s.hauer@pengutronix.de>,
	"Pengutronix Kernel Team" <kernel@pengutronix.de>,
	"Fabio Estevam" <festevam@gmail.com>,
	"NXP Linux Team" <linux-imx@nxp.com>,
	"Andreas Färber" <afaerber@suse.de>,
	"Manivannan Sadhasivam" <mani@kernel.org>,
	"Russell King" <linux@armlinux.org.uk>,
	"Florian Fainelli" <f.fainelli@gmail.com>,
	bcm-kernel-feedback-list@broadcom.com,
	"Pali Rohár" <pali@kernel.org>,
	"Kevin Cernekee" <cernekee@gmail.com>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Paul Walmsley" <paul.walmsley@sifive.com>,
	"Orson Zhai" <orsonzhai@gmail.com>,
	"Baolin Wang" <baolin.wang7@gmail.com>,
	"Chunyan Zhang" <zhang.lyra@gmail.com>,
	"Patrice Chotard" <patrice.chotard@foss.st.com>,
	linux-riscv@lists.infradead.org
Subject: Re: [PATCH v3 0/4] tty: TX helpers
Date: Wed, 7 Sep 2022 09:19:25 +0200	[thread overview]
Message-ID: <dec6d5c4-45b7-f087-95f4-bf1dae9e9d27@kernel.org> (raw)
In-Reply-To: <Yxcvbk281f/vy4vb@hovoldconsulting.com>

On 06. 09. 22, 13:30, Johan Hovold wrote:
> On Tue, Sep 06, 2022 at 12:48:01PM +0200, Jiri Slaby wrote:
>> This series introduces DEFINE_UART_PORT_TX_HELPER +
>> DEFINE_UART_PORT_TX_HELPER_LIMITED TX helpers. See PATCH 2/4 for the
>> details. Comments welcome.
>>
>> Then it switches drivers to use them. First, to
>> DEFINE_UART_PORT_TX_HELPER() in 3/4 and then
>> DEFINE_UART_PORT_TX_HELPER_LIMITED() in 4/4.
>>
>> The diffstat of patches 3+4 is as follows:
>>   26 files changed, 191 insertions(+), 823 deletions(-)
>> which appears to be nice.
> 
> Not really. This is horrid. Quality can't be measured in LoC (only).
> 
> The resulting code is unreadable. And for no good reason.

IMO, it's much more readable than the original ~ 30 various (and buggy 
-- see Ilpo's fixes) copies of this code. Apart from that, it makes 
further rework much easier (I have switch to kfifo in my mind for example).

> [ And note that you're "saving" something like 20 lines per driver:

It's not about saving, it's about deduplicating and unifying.

> 	 12 files changed, 84 insertions(+), 349 deletions(-)
> ]
> 
> NAK

I'd love to come up with something nicer. That would be a function in 
serial-core calling hooks like I had [1] for example. But provided all 
those CPU workarounds/thunks, it'd be quite expensive to call two 
functions per character.

Or creating a static inline (having ± the macro content) and the hooks 
as parameters and hope for optimizations to eliminate thunks (also 
suggested in the past [1]).

[1] https://lore.kernel.org/all/20220411105405.9519-1-jslaby@suse.cz/

thanks,
-- 
js
suse labs