linux-kernel - Re: [PATCH v2 2/3] usb: chipidea: Simplify Tegra DMA alignment code

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Message-ID: <ZShjNzj-8wR1f3qu@qmqm.qmqm.pl>
Date:   Thu, 12 Oct 2023 23:20:55 +0200
From:   Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Peter Geis <pgwipeout@...il.com>,
        Dmitry Osipenko <digetx@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Chen <peter.chen@...nel.org>,
        Thierry Reding <treding@...dia.com>,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH v2 2/3] usb: chipidea: Simplify Tegra DMA alignment code

On Wed, Oct 11, 2023 at 11:53:28PM +0200, Thierry Reding wrote:
> On Thu, Sep 28, 2023 at 11:06:03PM +0200, Michał Mirosław wrote:
> > The USB host on Tegra3 works with 32-bit alignment. Previous code tried
> > to align the buffer, but it did align the wrapper struct instead, so
> > the buffer was at a constant offset of 8 bytes (two pointers) from
> > expected alignment.  Since kmalloc() guarantees at least 8-byte
> > alignment already, the alignment-extending is removed.
> > 
> > Fixes: fc53d5279094 ("usb: chipidea: tegra: Support host mode")
> > Signed-off-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
> > ---
> >  drivers/usb/chipidea/host.c | 45 +++++++++++++++----------------------
> >  1 file changed, 18 insertions(+), 27 deletions(-)
> > 
> > diff --git a/drivers/usb/chipidea/host.c b/drivers/usb/chipidea/host.c
> > index abddd39d1ff1..0cce19208370 100644
> > --- a/drivers/usb/chipidea/host.c
> > +++ b/drivers/usb/chipidea/host.c
> > @@ -30,8 +30,7 @@ struct ehci_ci_priv {
> >  };
> >  
> >  struct ci_hdrc_dma_aligned_buffer {
> > -	void *kmalloc_ptr;
> > -	void *old_xfer_buffer;
> > +	void *original_buffer;
> >  	u8 data[];
> >  };
> >  
> > @@ -380,60 +379,52 @@ static int ci_ehci_bus_suspend(struct usb_hcd *hcd)
> >  	return 0;
> >  }
> >  
> > -static void ci_hdrc_free_dma_aligned_buffer(struct urb *urb)
> > +static void ci_hdrc_free_dma_aligned_buffer(struct urb *urb, bool copy_back)
> >  {
> >  	struct ci_hdrc_dma_aligned_buffer *temp;
> > -	size_t length;
> >  
> >  	if (!(urb->transfer_flags & URB_ALIGNED_TEMP_BUFFER))
> >  		return;
> > +	urb->transfer_flags &= ~URB_ALIGNED_TEMP_BUFFER;
> 
> This threw me off a bit until I realized it was already there
> previously, just in a different place. Is there a particular reason why
> this is moved?

I figured that it is easier to understand if the test and clear of the
URB_ALIGNED_TEMP_BUFFER bit is in a single place. Seeing it again, I
think it could be replaced with __test_and_clear_bit() in a future commit.

Best Regards
Michał Mirosław