linux-kernel - Re: [PATCH 1/3] mfd: Add realtek USB card reader driver

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Date:	Wed, 8 Jan 2014 16:03:06 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Roger Tseng <rogerable@...ltek.com>
Cc:	Samuel Ortiz <sameo@...ux.intel.com>,
	Lee Jones <lee.jones@...aro.org>, Chris Ball <cjb@...top.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Maxim Levitsky <maximlevitsky@...il.com>,
	Alex Dubov <oakad@...oo.com>,
	"driverdev-devel@...uxdriverproject.org" 
	<driverdev-devel@...uxdriverproject.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Wei_wang <wei_wang@...lsil.com.cn>
Subject: Re: [PATCH 1/3] mfd: Add realtek USB card reader driver

On Wed, Jan 08, 2014 at 03:56:05PM +0800, Roger Tseng wrote:
> Hi Dan,
> 
> >> +int rtsx_usb_ep0_write_register(struct rtsx_ucr *ucr, u16 addr,
> >> +             u8 mask, u8 data)
> >> +{
> >> +     u16 value = 0, index = 0;
> >> +
> >> +     value |= (u16)(3 & 0x03) << 14;
> >> +     value |= (u16)(addr & 0x3FFF);
> >
> >Don't do pointless things:
> >
> >        value |= 0x03 << 14;
> >        value |= addr & 0x3FFF;
> >
> >> +     value = ((value << 8) & 0xFF00) | ((value >> 8) & 0x00FF);
> >
> >This is an endian conversion?  It is buggy.  Use the kernel endian
> >conversion functions cpu_to_le16().
> 
> This is not a conversion for endianess with respect to CPU but for
> command format  of the device. It should always be performed
> regardless of platform.
> 
> In other words, it could be equivalent to:
>         value |= 0x03 << 6; // lower byte
>         value |= (addr & 0x3F00) >> 8; // lower byte
>         value |= (addr & 0xFF) << 8; //higher byte
> 
> We think the previous form is easier to read. Should we keep it or
> change to the later one?

To me it's really weird that the standard would specify that the address
is in byte swapped reversed CPU-endian order.  But if that's what it
says then I don't care about formatting details.  The original code is
fine.

regards,
dan carpenter
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