Re: [PATCH v5 2/4] drivers/tty/serial/8250: refactor sirq and lpc address setting code

From: "Andrew Jeffery" <andrew@aj.id.au>
To: linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v5 2/4] drivers/tty/serial/8250: refactor sirq and lpc address setting code
Date: Fri, 09 Apr 2021 16:41:23 +0930	[thread overview]
Message-ID: <f0dd410b-53af-400d-ba79-334c55eff854@beta.fastmail.com> (raw)
In-Reply-To: <YG/7sFv+2AlLKbZ5@hatter.bewilderbeest.net>

On Fri, 9 Apr 2021, at 16:31, Zev Weiss wrote:
> On Fri, Apr 09, 2021 at 12:06:16AM CDT, Andrew Jeffery wrote:
> >
> >
> >On Thu, 8 Apr 2021, at 10:46, Zev Weiss wrote:
> >> This splits dedicated aspeed_vuart_set_{sirq,lpc_address}() functions
> >> out of the sysfs store functions in preparation for adding DT
> >> properties that will be poking the same registers.  While we're at it,
> >> these functions now provide some basic bounds-checking on their
> >> arguments.
> >>
> >> Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
> >> ---
> >>  drivers/tty/serial/8250/8250_aspeed_vuart.c | 51 ++++++++++++++-------
> >>  1 file changed, 35 insertions(+), 16 deletions(-)
> >>
> >> diff --git a/drivers/tty/serial/8250/8250_aspeed_vuart.c
> >> b/drivers/tty/serial/8250/8250_aspeed_vuart.c
> >> index c33e02cbde93..8433f8dbb186 100644
> >> --- a/drivers/tty/serial/8250/8250_aspeed_vuart.c
> >> +++ b/drivers/tty/serial/8250/8250_aspeed_vuart.c
> >> @@ -72,22 +72,31 @@ static ssize_t lpc_address_show(struct device *dev,
> >>  	return snprintf(buf, PAGE_SIZE - 1, "0x%x\n", addr);
> >>  }
> >>
> >> +static int aspeed_vuart_set_lpc_address(struct aspeed_vuart *vuart, u32 addr)
> >> +{
> >> +	if (addr > U16_MAX)
> >> +		return -EINVAL;
> >> +
> >> +	writeb(addr >> 8, vuart->regs + ASPEED_VUART_ADDRH);
> >> +	writeb(addr >> 0, vuart->regs + ASPEED_VUART_ADDRL);
> >> +
> >> +	return 0;
> >> +}
> >> +
> >>  static ssize_t lpc_address_store(struct device *dev,
> >>  				 struct device_attribute *attr,
> >>  				 const char *buf, size_t count)
> >>  {
> >>  	struct aspeed_vuart *vuart = dev_get_drvdata(dev);
> >> -	unsigned long val;
> >> +	u32 val;
> >>  	int err;
> >>
> >> -	err = kstrtoul(buf, 0, &val);
> >> +	err = kstrtou32(buf, 0, &val);
> >>  	if (err)
> >>  		return err;
> >>
> >> -	writeb(val >> 8, vuart->regs + ASPEED_VUART_ADDRH);
> >> -	writeb(val >> 0, vuart->regs + ASPEED_VUART_ADDRL);
> >> -
> >> -	return count;
> >> +	err = aspeed_vuart_set_lpc_address(vuart, val);
> >> +	return err ? : count;
> >>  }
> >>
> >>  static DEVICE_ATTR_RW(lpc_address);
> >> @@ -105,27 +114,37 @@ static ssize_t sirq_show(struct device *dev,
> >>  	return snprintf(buf, PAGE_SIZE - 1, "%u\n", reg);
> >>  }
> >>
> >> +static int aspeed_vuart_set_sirq(struct aspeed_vuart *vuart, u32 sirq)
> >> +{
> >> +	u8 reg;
> >> +
> >> +	if (sirq > (ASPEED_VUART_GCRB_HOST_SIRQ_MASK >> ASPEED_VUART_GCRB_HOST_SIRQ_SHIFT))
> >> +		return -EINVAL;
> >> +
> >> +	sirq <<= ASPEED_VUART_GCRB_HOST_SIRQ_SHIFT;
> >> +	sirq &= ASPEED_VUART_GCRB_HOST_SIRQ_MASK;
> >
> >This might be less verbose if we reordered things a little:
> >
> >```
> >sirq <<= ASPEED_VUART_GCRB_HOST_SIRQ_SHIFT;
> >if (sirq & ASPEED_VUART_GCRB_HOST_SIRQ_MASK)
> >	return -EINVAL;
> >sirq &= ASPEED_VUART_GCRB_HOST_SIRQ_MASK;
> >```
> 
> Hmm, that (or something similar, perhaps with a '~' on the mask in the 
> if condition?) does seem like it'd be a nice improvement, though I 
> suppose it'd also mean we'd fail to reject some way-out-of-range sirq 
> values (e.g. if it had its MSB set) -- so I think I'll leave it as is, 
> just in the name of thoroughness/paranoia?

Yeah, fair enough. I was considering smaller errors :)

Andrew

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