Re: [PATCH v2] PCI/VPD: Use unaligned access helpers in pci_vpd_read

[Heiner Kallweit <hkallweit1@gmail.com>]

On 10.05.2021 08:36, Christoph Hellwig wrote:
> On Sat, May 08, 2021 at 12:29:15AM +0200, Heiner Kallweit wrote:
>> +
>> +		if (len == 4)  {
>> +			put_unaligned_le32(val, buf);
>> +		} else {
>> +			cpu_to_le32s(&val);
>> +			memcpy(buf, (u8 *)&val + skip, len);
> 
> cpu_to_le32s is a horrible API that breaks endianess annotations.
> 
The endian-adjusted value is used just in the next line, so I think
there's no risk of wrong usage.
But yes, this function converts to le32 w/o using __bitwise.
Therefore I understand the concern.

> Is the intent of this code to only put 16 bits in?  Why not something
> like:
> 
> 		switch (len) {
> 		case 4:
> 			put_unaligned_le32(val, buf);
> 			break;
> 		case 2:
> 			put_unaligned_le16(val, buf + 2);
> 			break;
> 		case 1:
> 			buf[3] = val;
> 			break;
>   		}
> 
len can have any value 1 .. 4. Also the proposal doesn't consider
the skip value.