linux-kernel - RE: [PATCH] tty: serial: imx: initialize peripheral_config/peripheral

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Message-ID: <AS8PR04MB8404990740869737F326D302929C9@AS8PR04MB8404.eurprd04.prod.outlook.com>
Date:   Wed, 3 Aug 2022 09:15:58 +0000
From:   Sherry Sun <sherry.sun@....com>
To:     Ahmad Fatoum <a.fatoum@...gutronix.de>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "jirislaby@...nel.org" <jirislaby@...nel.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH] tty: serial: imx: initialize
 peripheral_config/peripheral_size for sdma config

> On 03.08.22 08:57, Sherry Sun wrote:
> > Since commit 824a0a02cd74 ("dmaengine: imx-sdma: Add multi fifo
> > support") adds the use of
> > dma_slave_config->peripheral_config/peripheral_size to sdma driver,
> > the client drivers like uart need to initialize the
> > peripheral_config/peripheral_size for sdma, otherwise, the random
> > value of local variable slave_config may cause unexpected
> peripheral_config and make sdma mess up.
> >
> 
> If this a fix, please add a Fixes: tag. I am not sure it is though, see below.

Hi Ahmad, thanks for the comments.
I don't think this patch is a fix for a specific commit, so we don't need the Fixes tag.

> 
> > Signed-off-by: Sherry Sun <sherry.sun@....com>
> > ---
> >  drivers/tty/serial/imx.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c index
> > 522445a8f666..bb8c2a712e94 100644
> > --- a/drivers/tty/serial/imx.c
> > +++ b/drivers/tty/serial/imx.c
> > @@ -1320,6 +1320,8 @@ static int imx_uart_dma_init(struct imx_port
> > *sport)
> 
> This function starts with
> 
> struct dma_slave_config slave_config = {};
> 
> >  	slave_config.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
> >  	/* one byte less than the watermark level to enable the aging timer
> */
> >  	slave_config.src_maxburst = RXTL_DMA - 1;
> > +	slave_config.peripheral_config = NULL;
> > +	slave_config.peripheral_size = 0;
> 
> So these are already zero-initialized.

I am not sure actually, I think initialize a struct with {} cannot guarantee that all members are initialized to 0, it may depend on the compiler.

Best regards
Sherry

> 
> >  	ret = dmaengine_slave_config(sport->dma_chan_rx, &slave_config);
> >  	if (ret) {
> >  		dev_err(dev, "error in RX dma configuration.\n"); @@ -
> 1346,6
> > +1348,8 @@ static int imx_uart_dma_init(struct imx_port *sport)
> >  	slave_config.dst_addr = sport->port.mapbase + URTX0;
> >  	slave_config.dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
> >  	slave_config.dst_maxburst = TXTL_DMA;
> > +	slave_config.peripheral_config = NULL;
> > +	slave_config.peripheral_size = 0;
> 
> Not sure if this is required. If preceding dmaengine_slave_config() indeed
> makes clearing necessary, you should note that in the commit message.
>