Re: [PATCH 2/2] spi: sh-msiof: Use DMA if possible

From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Nguyen An Hoan <na-hoan@jinso.co.jp>
Cc: Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
	"Mark Brown" <broonie@kernel.org>,
	"Geert Uytterhoeven" <geert+renesas@glider.be>,
	"Magnus Damm" <magnus.damm@gmail.com>,
	linux-spi <linux-spi@vger.kernel.org>,
	"Kuninori Morimoto" <kuninori.morimoto.gx@renesas.com>,
	"Yoshihiro Shimoda" <yoshihiro.shimoda.uh@renesas.com>,
	稲吉 <h-inayoshi@jinso.co.jp>, Dung：人ソ <nv-dung@jinso.co.jp>,
	カオ・ヴァン・ドン <cv-dong@jinso.co.jp>
Subject: Re: [PATCH 2/2] spi: sh-msiof: Use DMA if possible
Date: Fri, 11 Jan 2019 10:09:10 +0100	[thread overview]
Message-ID: <CAMuHMdUAk004J-06o43yHei10tWCkyztsWUXUyCj36cPwT9D0w@mail.gmail.com> (raw)
In-Reply-To: <1547197109-637-2-git-send-email-na-hoan@jinso.co.jp>

Hi Hoan-san,

On Fri, Jan 11, 2019 at 9:59 AM Nguyen An Hoan <na-hoan@jinso.co.jp> wrote:
> From: Hoan Nguyen An <na-hoan@jinso.co.jp>
>
> Currently, this driver only supports feature for DMA 32-bits.
> In this case, only if the data length is divisible by 4 to use
> DMA, otherwise PIO will be used. This patch will suggest use
> the DMA 32-bits with 4bytes of words, then the remaining data
> will be transmitted by PIO mode.
>
> Signed-off-by: Hoan Nguyen An <na-hoan@jinso.co.jp>

Thanks for your patch, that's a great idea!

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
with a small suggestion below.

> --- a/drivers/spi/spi-sh-msiof.c
> +++ b/drivers/spi/spi-sh-msiof.c
> @@ -937,17 +937,13 @@ static int sh_msiof_transfer_one(struct spi_master *master,
>                 unsigned int l = 0;
>
>                 if (tx_buf)
> -                       l = min(len, p->tx_fifo_size * 4);
> +                       l = min(len - len % 4, p->tx_fifo_size * 4);

I think this would be easier to read when written as:

    l = min(round_down(len, 4), p->tx_fifo_size * 4);

>                 if (rx_buf)
> -                       l = min(len, p->rx_fifo_size * 4);
> +                       l = min(len - len % 4, p->rx_fifo_size * 4);

Likewise,

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds