linux-kernel - Re: [PATCH v4 08/10] tty: serial: introduce transmit helpers

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Date:   Tue, 20 Sep 2022 11:43:04 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Jiri Slaby <jslaby@...e.cz>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-serial <linux-serial@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 08/10] tty: serial: introduce transmit helpers

On Tue, 20 Sep 2022, Jiri Slaby wrote:

> Many serial drivers do the same thing:
> * send x_char if set
> * keep sending from the xmit circular buffer until either
>   - the loop reaches the end of the xmit buffer
>   - TX is stopped
>   - HW fifo is full
> * check for pending characters and:
>   - wake up tty writers to fill for more data into xmit buffer
>   - stop TX if there is nothing in the xmit buffer
> 
> The only differences are:
> * how to write the character to the HW fifo
> * the check of the end condition:
>   - is the HW fifo full?
>   - is limit of the written characters reached?
> 
> So unify the above into two helpers:
> * uart_port_tx_limited() -- it performs the above taking the written
>   characters limit into account, and
> * uart_port_tx() -- the same as above, except it only checks the HW
>   readiness, not the characters limit.
> 
> The HW specific operations (as stated as "differences" above) are passed
> as arguments to the macros. They are:
> * tx_ready -- returns true if HW can accept more data.
> * put_char -- write a character to the device.
> * tx_done -- when the write loop is done, perform arbitrary action
>   before potential invocation of ops->stop_tx() happens.
> 
> Note that the above are macros. This means the code is generated in
> place and the above 3 arguments are "inlined". I.e. no added penalty by
> generating call instructions for every single character. Nor any
> indirect calls. (As in some previous versions of this patchset.)
> 
> Signed-off-by: Jiri Slaby <jslaby@...e.cz>

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>

-- 
 i.