linux-kernel - Re: [PATCH v12 6/6] fpga-manager: altera-ps-spi: use bitrev8x4

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Date:   Mon, 5 Jun 2017 10:13:07 -0500
From:   Alan Tull <atull@...nel.org>
To:     Joshua Clayton <stillcompiling@...il.com>
Cc:     Moritz Fischer <moritz.fischer@...us.com>,
        Anatolij Gustschin <agust@...x.de>,
        Bastian Stender <bst@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Sascha Hauer <kernel@...gutronix.de>,
        Fabio Estevam <fabio.estevam@....com>,
        Russell King <linux@...linux.org.uk>,
        linux-fpga@...r.kernel.org,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v12 6/6] fpga-manager: altera-ps-spi: use bitrev8x4

On Fri, Jun 2, 2017 at 3:30 PM, Joshua Clayton <stillcompiling@...il.com> wrote:

Hi Joshua,

Thanks for your work on this!

Alan

> Speed up bit reversal by using hardware bit reversal
> Add extra code to handle less than 4byte remnants, if any
>
> Signed-off-by: Joshua Clayton <stillcompiling@...il.com>

Signed-off-by: Alan Tull <atull@...nel.org>

> ---
>  drivers/fpga/altera-ps-spi.c | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/fpga/altera-ps-spi.c b/drivers/fpga/altera-ps-spi.c
> index 0db8def668ed..14f14efdf0d5 100644
> --- a/drivers/fpga/altera-ps-spi.c
> +++ b/drivers/fpga/altera-ps-spi.c
> @@ -149,12 +149,23 @@ static int altera_ps_write_init(struct fpga_manager *mgr,
>
>  static void rev_buf(char *buf, size_t len)
>  {
> -       const char *fw_end = (buf + len);
> +       u32 *fw32 = (u32 *)buf;
> +       size_t extra_bytes = (len & 0x03);
> +       const u32 *fw_end = (u32 *)(buf + len - extra_bytes);
>
>         /* set buffer to lsb first */
> -       while (buf < fw_end) {
> -               *buf = bitrev8(*buf);
> -               buf++;
> +       while (fw32 < fw_end) {
> +               *fw32 = bitrev8x4(*fw32);
> +               fw32++;
> +       }
> +
> +       if (extra_bytes) {
> +               buf = (char *)fw_end;
> +               while (extra_bytes) {
> +                       *buf = bitrev8(*buf);
> +                       buf++;
> +                       extra_bytes--;
> +               }
>         }
>  }
>
> --
> 2.11.0
>