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From: Haavard Skinnemoen <>
To: Ben Nizette <>
	Linux Kernel list <>,
	kernel <>,
Subject: Re: [PATCH] atmel_spi: fix dma addr calculation for len > BUFFER_SIZE
Date: Mon, 28 Sep 2009 09:12:59 +0200	[thread overview]
Message-ID: <20090928091259.27485716@hskinnemoen-d830> (raw)
In-Reply-To: <1254029187.7587.146.camel@ben-desktop>

Ben Nizette <> wrote:
> If len > BUFFER_LEN and !xfer->rx_buf we end up calculating the tx
> buffer address as
> *tx_dma = xfer->tx_dma + xfer->len - BUFFER_SIZE;
> which is constant; i.e. we just send the last BUFFER_SIZE data over
> again until we've reached the right number of bytes.
> This patch gets around this by using the /requested/ length when
> calculating addresses.
> Note there's no way len != *plen when we calculate the rx buffer address
> but conceptually we should be using *plen and I don't want someone to
> come through later, see the calculations for rx and tx are different and
> "clean up" back to what we had.
> Signed-off-by: Ben Nizette <>

Wow, that is subtle. I had to stare at it for a long while before I
understood what's going on, but I believe you're right.

Acked-by: Haavard Skinnemoen <>

While you're at it, could you send another patch renaming 'len' to
'next_len'? I think that would make it a bit more obvious why your
patch is correct and prevent similar mistakes in the future.


  reply	other threads:[~2009-09-28  7:12 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-09-27  5:26 [PATCH] atmel_spi: fix dma addr calculation for len > BUFFER_SIZE Ben Nizette
2009-09-28  7:12 ` Haavard Skinnemoen [this message]
2009-09-29  0:55   ` Ben Nizette
2009-09-29  6:57     ` Haavard Skinnemoen

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