linux-kernel - Re: [PATCH] usb: renesas_usbhs: fix _

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Message-ID: <CAMuHMdWsRDyUh0MzYNX=mQuuPem1NxArFOqXGVAba3TWGEXxWg@mail.gmail.com>
Date:   Thu, 17 Oct 2019 08:57:26 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Simon Horman <horms@...ge.net.au>
Cc:     "linux-kernel@...ts.codethink.co.uk" 
        <linux-kernel@...ts.codethink.co.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Ben Dooks (Codethink)" <ben.dooks@...ethink.co.uk>
Subject: Re: [PATCH] usb: renesas_usbhs: fix __le16 warnings

Hi Shimoda-san, Simon,

On Thu, Oct 17, 2019 at 4:18 AM Yoshihiro Shimoda
<yoshihiro.shimoda.uh@...esas.com> wrote:
> > From: Simon Horman, Sent: Wednesday, October 16, 2019 9:27 PM
> <snip>
> > > diff --git a/drivers/usb/renesas_usbhs/common.c b/drivers/usb/renesas_usbhs/common.c
> > > index 4c3de777ef6c..a3c30b609433 100644
> > > --- a/drivers/usb/renesas_usbhs/common.c
> > > +++ b/drivers/usb/renesas_usbhs/common.c
> > > @@ -162,17 +162,17 @@ void usbhs_usbreq_get_val(struct usbhs_priv *priv, struct usb_ctrlrequest *req)
> > >     req->bRequest           = (val >> 8) & 0xFF;
> > >     req->bRequestType       = (val >> 0) & 0xFF;
> > >
> > > -   req->wValue     = usbhs_read(priv, USBVAL);
> > > -   req->wIndex     = usbhs_read(priv, USBINDX);
> > > -   req->wLength    = usbhs_read(priv, USBLENG);
> > > +   req->wValue     = cpu_to_le16(usbhs_read(priv, USBVAL));
> > > +   req->wIndex     = cpu_to_le16(usbhs_read(priv, USBINDX));
> > > +   req->wLength    = cpu_to_le16(usbhs_read(priv, USBLENG));
> >
> > usbhs_read is backed by readl which performs
> > a le->cpu conversion. Rather than have a double conversion
> > perhaps it would be nicer to introduce usbhs_read_le.
> > Likewise for write.
>
> I'm afraid but, I could not understand these comments.
> At the moment, the usbhs_{read,write}() call io{read,write}16(),
> not {read,write}l().
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/usb/renesas_usbhs/common.c?h=v5.4-rc3#n62

ioread16() and readw() don't do byteswapping on ARM, as ARM is
little-endian. Likewise, cpu_to_le16() is a no-op on ARM.

Double swapping would matter only on a big-endian platform, and could
indeed be avoided by introducing usbhs_read_le*() functions that are
just wrappers around __raw_read16() on big-endian.
However, until the Renesas USBHS IP core ends up on a big-endian
platform, it's not worth doing that, IMHO.

> > >  }
> > >
> > >  void usbhs_usbreq_set_val(struct usbhs_priv *priv, struct usb_ctrlrequest *req)
> > >  {
> > >     usbhs_write(priv, USBREQ,  (req->bRequest << 8) | req->bRequestType);
> > > -   usbhs_write(priv, USBVAL,  req->wValue);
> > > -   usbhs_write(priv, USBINDX, req->wIndex);
> > > -   usbhs_write(priv, USBLENG, req->wLength);
> > > +   usbhs_write(priv, USBVAL,  le16_to_cpu(req->wValue));
> > > +   usbhs_write(priv, USBINDX, le16_to_cpu(req->wIndex));
> > > +   usbhs_write(priv, USBLENG, le16_to_cpu(req->wLength));
> > >
> > >     usbhs_bset(priv, DCPCTR, SUREQ, SUREQ);
> > >  }

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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