On 10/26/2012 05:33 AM, Vikram Narayanan wrote:
> Some nitpicks.
>
> On 10/24/2012 10:20 AM, Stephen Warren wrote:
>> This adds a simple driver for the BCM2835's SD controller.
>>
>> Workarounds are implemented for:
>> * Register writes can't be too close to each-other in time, or they will
>> be lost.
>> * Register accesses must all be 32-bit, so implement custom accessors.
...
>> +static u8 bcm2835_sdhci_readb(struct sdhci_host *host, int reg)
>> +{
>> + u32 val = bcm2835_sdhci_raw_readl(host, (reg& ~3));
>> + val = val>> (reg<< 3& 0x18)& 0xff;
>> +
>> + return (u8)val;
>> +}
>
> Can the above used magics be made as macros?
This code was taken directly from the downstream Linux kernel, so I
changed it as little as possible, to make comparisons easier. Still, if
people want I can certainly make it easier to understand the expression
a bit.
I don't think the issue is the magic numbers so much as understanding
what the expression does; the magic are obvious then. It's simply
extracting byte n from from a u32. Would the following be more obvious:
byte_num = reg & 3;
byte_shift = bytenum * 8;
byte = (val >> byte_shift) & 0xff;
... and similar for the other functions?
_______________________________________________
U-Boot mailing list
U-Boot@lists.denx.de
http://lists.denx.de/mailman/listinfo/u-boot
