linux-kernel - Re: [PATCH 09/11] spi-dw: Fix condition in spi_dw

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Message-ID: <20110623112552.6f22c3de@feng-i7>
Date:	Thu, 23 Jun 2011 11:25:52 +0800
From:	Feng Tang <feng.tang@...el.com>
To:	Dirk Brandewie <dirk.brandewie@...il.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"spi-devel-general@...ts.sourceforge.net" 
	<spi-devel-general@...ts.sourceforge.net>
Subject: Re: [PATCH 09/11] spi-dw: Fix condition in spi_dw_{writer/reader}

On Thu, 23 Jun 2011 11:09:34 +0800
Dirk Brandewie <dirk.brandewie@...il.com> wrote:

> On 06/22/2011 07:45 PM, Feng Tang wrote:
> > On Thu, 23 Jun 2011 10:00:11 +0800
> > "dirk.brandewie@...il.com"<dirk.brandewie@...il.com>  wrote:
> >
> >> From: Dirk Brandewie<dirk.brandewie@...il.com>
> >>
> >> Fix the condition based on whether the current transfer has a tx/rx
> >> buffer.
> >>
> >> Signed-off-by: Dirk Brandewie<dirk.brandewie@...il.com>
> >> ---
> >>   drivers/spi/spi-dw.c |    6 +++---
> >>   1 files changed, 3 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/spi/spi-dw.c b/drivers/spi/spi-dw.c
> >> index cc38aa0..35b952b 100644
> >> --- a/drivers/spi/spi-dw.c
> >> +++ b/drivers/spi/spi-dw.c
> >> @@ -193,8 +193,8 @@ static void spi_dw_writer(struct spi_dw *dws)
> >>   	u16 txw = 0;
> >>
> >>   	while (max--) {
> >> -		/* Set the tx word if the transfer's original "tx"
> >> is not null */
> >> -		if (dws->tx_end - dws->len) {
> >> +		/* Set the tx word if the transfer's "tx" is not
> >> null */
> >> +		if (dws->tx) {
> >
> > No, in current mainstream code, the dws->tx is changing, see code:
> > 	dws->tx += dws->n_bytes;
> > so we have to use if (dws->tx_end - dws->len) for now, maybe
> > we can use some bit to indicate whether the original tx is null
> 
> If dws->tx is non-null then it points to a valid buffer, it is
> unconditionally set with dws->tx = (void *)transfer->tx_buf when the
> transfer is setup.  if the original transfer->tx_buf is non-null then
> this change works.

dws->tx is changing as I said, non-null doesn't mean the value is valid,
when the original tx is null, we don't access it at all, it's just a
indicator of whether the dws->len of zeor has been filled to FIFO.

This logic may looks confusing, but it's correct after years of test.

> 
> >
> >>   			if (dws->n_bytes == 1)
> >>   				txw = *(u8 *)(dws->tx);
> >>   			else
> >> @@ -213,7 +213,7 @@ static void spi_dw_reader(struct spi_dw *dws)
> >>   	while (max--) {
> >>   		rxw = dw_readw(dws, dr);
> >>   		/* Care rx only if the transfer's original "rx"
> >> is not null */
> >> -		if (dws->rx_end - dws->len) {
> >> +		if (dws->rx) {
> >>   			if (dws->n_bytes == 1)
> >>   				*(u8 *)(dws->rx) = rxw;
> >>   			else
> 
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