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

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Date:   Mon, 10 Jan 2022 19:44:19 +0100
From:   Pavel Machek <pavel@...x.de>
To:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc:     Cezary Rojewski <cezary.rojewski@...el.com>,
        Biju Das <biju.das.jz@...renesas.com>,
        Pavel Machek <pavel@...x.de>,
        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

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.
> 
> > Please note that refactoring below function into while-loop has a side
> > effect: everything had to be indented by additional tab. Generally,
> > readability increases if function is shaped 'linearly'.
> >
> I do agree, my initial patch just added a jump back to the start of
> the function if there are more samples, but Biju suggested to use a
> while loop instead.

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.

Best regards,
								Pavel

-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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