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

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Date:   Wed, 3 Aug 2022 09:51:00 +0000
From:   Sherry Sun <sherry.sun@....com>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
CC:     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>,
        "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


> Subject: Re: [PATCH] tty: serial: imx: initialize
> peripheral_config/peripheral_size for sdma config
> 
> On Wed, Aug 03, 2022 at 09:15:58AM +0000, Sherry Sun wrote:
> > > 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.
> 
> I'm sure and even reverified in my C book[1].
> 
> 	struct mystruct variable = {};
> 
> results in all components being initialized to their default initial value (which
> is 0 for numbers and NULL for pointers). This works for automatic variables
> since "Standard C" which should cover everthing that is capable to compile
> today's kernel.
> 
> Best regards
> Uwe
> 
> [1] C - A Reference Manual, 978-0130895929
> 

Hi Uwe, wow, this really resolved my confusion, thanks a lot for your confirmation! ^_^

Best regards
Sherry