linux-kernel - Re: [PATCH 1/5] ASoC: sh: rz-ssi: Drop calling rz_ssi_pio

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Date:   Mon, 10 Jan 2022 19:58:01 +0100
From:   Cezary Rojewski <cezary.rojewski@...el.com>
To:     Pavel Machek <pavel@...x.de>,
        "Lad, Prabhakar" <prabhakar.csengg@...il.com>
CC:     Biju Das <biju.das.jz@...renesas.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        alsa-devel <alsa-devel@...a-project.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/5] ASoC: sh: rz-ssi: Drop calling rz_ssi_pio_recv()
 recursively

On 2022-01-10 7:44 PM, Pavel Machek wrote:
> Hi!
> 
>>> On 2022-01-10 10:47 AM, Lad Prabhakar wrote:
>>>> Instead of recursively calling rz_ssi_pio_recv() use a while loop
>>>> to read the samples from RX fifo.
>>>
>>> Recursion and loops are means for doing something repeatedly. Could you
>>> specify _why_ such change was made i.e. the conversion from one method
>>> into the other? I bet the code is not being changed for the sake of
>>> changing it, the reason is simply missing in the commit message.
>>>
>> I had feedback from Pavel "recursion is unwelcome in kernel due to
>> limited stack use." which I did agree with as a result I have come up
>> with this patch. Also to add this driver will later be used on Renesas
>> RZ/A2 SoC's which runs with limited memory.

...

> 
> Yes, loop is better.
> 
> I'd actually do while(true) and avoid using the done variable.
> 
>      if (!(!frames_left && fifo_samples >= runtime->channels))
>                break;
> 
> will do the trick. Better yet, do
> 
>      if (frames_left || fifo_samples < runtime->channels)
>                break;
> 
> because double negation is quite confusing and looks like typo.

You could achieve similar results by enlisting do-while loop. That's my 
proposal.


Regards,
Czarek