Re: [PATCH] libata: warn if speed limited due to 40-wire cable (v2)

[Stephen Clark <Stephen.Clark@seclark.us>]

Bill Davidsen wrote:

>Stephen Clark wrote:
>  
>
>>Bill Davidsen wrote:
>>
>>    
>>
>>>Alan Cox wrote:
>>> 
>>>
>>>      
>>>
>>>>>it seems broken to manipulate xfer_mask after returning from the 
>>>>>driver's ->mode_filter hook.
>>>>>
>>>>>this patch is more than just a speed-limited warning printk, afaics
>>>>>    
>>>>>          
>>>>>
>>>>I actually suggested that order because the only way the printk can be
>>>>done correctly is for it to be the very last test made. Since the mode
>>>>filter is not told what mode will be used but just subtracts modes that
>>>>are not allowed this should be safe.
>>>>  
>>>>        
>>>>
>>>Far better to have a drive which works slowly than one which works 
>>>unreliably.
>>>
>>> 
>>>
>>>      
>>>
>>That would be true if the 40 wire detection was 100% accurate!
>>    
>>
>The statement is completely correct, even though the detection may not 
>be. ;-)
>
>With the current set(s) of patches to do better detection, cable 
>evaluation should be better. But even if not, a slow system is more 
>useful than one which doesn't work, crashes because of swap i/o errors, etc.
>
>  
>
I have had problems with cable detection on my previous laptop and my 
current laptop. It almost made
my systems unusable. On my current laptop I was getting a thruput of a 
little over 1 mbps instead
of the 44 mbps I get with udma set to the correct value. It took hours 
to upgrade my laptop from
fc5 to fc6 because of this mis detection.

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