linux-kernel - Re: [PATCH] staging: wimax/i2400m: don't change the endianness of one byte variable

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Date:   Thu, 18 Feb 2021 14:54:28 +0500
From:   Muhammad Usama Anjum <musamaanjum@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     lee.jones@...aro.org, johannes@...solutions.net, arnd@...db.de,
        kuba@...nel.org, gustavoars@...nel.org, wanghai38@...wei.com,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        musamaanjum@...il.com
Subject: Re: [PATCH] staging: wimax/i2400m: don't change the endianness of
 one byte variable

On Thu, 2021-02-18 at 10:40 +0100, Greg KH wrote:
> On Thu, Feb 18, 2021 at 02:21:54PM +0500, Muhammad Usama Anjum wrote:
> > It is wrong to change the endianness of a variable which has just one
> > byte size.
> > 
> > Sparse warnings fixed:
> > drivers/staging//wimax/i2400m/control.c:452:17: warning: cast to restricted __le32
> > drivers/staging//wimax/i2400m/control.c:452:17: warning: cast to restricted __le32
> > drivers/staging//wimax/i2400m/op-rfkill.c:159:14: warning: cast to restricted __le32
> > drivers/staging//wimax/i2400m/op-rfkill.c:160:14: warning: cast to restricted __le32
> > 
> > Signed-off-by: Muhammad Usama Anjum <musamaanjum@...il.com>
> > ---
> >  drivers/staging/wimax/i2400m/control.c   | 4 ++--
> >  drivers/staging/wimax/i2400m/op-rfkill.c | 4 ++--
> >  2 files changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/staging/wimax/i2400m/control.c b/drivers/staging/wimax/i2400m/control.c
> > index 1e270b2101e8..b6b2788af162 100644
> > --- a/drivers/staging/wimax/i2400m/control.c
> > +++ b/drivers/staging/wimax/i2400m/control.c
> > @@ -452,8 +452,8 @@ void i2400m_report_state_parse_tlv(struct i2400m *i2400m,
> >  		d_printf(2, dev, "%s: RF status TLV "
> >  			 "found (0x%04x), sw 0x%02x hw 0x%02x\n",
> >  			 tag, I2400M_TLV_RF_STATUS,
> > -			 le32_to_cpu(rfss->sw_rf_switch),
> > -			 le32_to_cpu(rfss->hw_rf_switch));
> > +			 rfss->sw_rf_switch,
> > +			 rfss->hw_rf_switch);
> 
> What do you mean by "one byte"?  This is a le32 sized variable, right?
> If not, why isn't the le32_to_cpu() call complaining?

These two variables are of type _u8, one byte. 
	__u8 sw_rf_switch;
	__u8 hw_rf_switch;
They aren't of type __le32. le32_to_cpu() macro should have
complained. But it isn't complaining. It seems like whatever we pass
to this macro, it casts it to __le32 forcefully (it seems like wrong).
So we'll never get any complain from this macro directly. But we are
getting complain from the sparse.

For big endian:
#define __le32_to_cpu(x) __swab32((__force __u32)(__le32)(x))
For little endian:
#define __le32_to_cpu(x) ((__force __u32)(__le32)(x))

> >  		i2400m_report_tlv_rf_switches_status(i2400m, rfss);
> >  	}
> >  	if (0 == i2400m_tlv_match(tlv, I2400M_TLV_MEDIA_STATUS, sizeof(*ms))) {
> > diff --git a/drivers/staging/wimax/i2400m/op-rfkill.c b/drivers/staging/wimax/i2400m/op-rfkill.c
> > index fbddf2e18c14..a159808f0ec2 100644
> > --- a/drivers/staging/wimax/i2400m/op-rfkill.c
> > +++ b/drivers/staging/wimax/i2400m/op-rfkill.c
> > @@ -156,8 +156,8 @@ void i2400m_report_tlv_rf_switches_status(
> >  	enum i2400m_rf_switch_status hw, sw;
> >  	enum wimax_st wimax_state;
> >  
> > -	sw = le32_to_cpu(rfss->sw_rf_switch);
> > -	hw = le32_to_cpu(rfss->hw_rf_switch);
> > +	sw = rfss->sw_rf_switch;
> > +	hw = rfss->hw_rf_switch;
> 
> Same here.

Same here.

> thanks,
> 
> greg k-h