Re: [PATCH] Add hook for custom xfer function in PATA Platform driver

[Sergei Shtylyov <sshtylyov@mvista.com>]

Hello.

Graeme Russ wrote:

> [Added linux-ide back onto distribution list]
>   

   Right, I didn't intend to exclude it -- probably didn't press all the 
keys at once for the reply-to-all function.

[...]
>
>>   You should have also taught the symmetric ide-platfrom driver the same
>> trick. However, IDE core's data transfer methods has a different prototype.
>>     
>
> I did think about the other drivers (OF Platform etc) but I have no way of
> testing them.
>   

   pata_of_platform is not easily extensible in this way. It gets all 
the information about the device from the device tree -- and you can't 
encode all your complications there, unless you invent a new OF device.

>> I suggest to rather add a new flag, indicating 8-bit data I/O, and have
>> the alternate sff_data_xfer() method defined inside the driver.
>>
>>     
>
> Well actually it goes beyond simply implementing 8-bit data transfers - On
> my particular board, the PATA devices (2x CF slots) are on a General
> Purpose Bus with a few other peripherals. The timing requirements for the
> bus when accessing the CF cards are very strict (and very slow compared to
> other devices on the bus). By overriding the data transfer function I can
> arbitrate access to the bus and switch the bus timings based on the
> peripheral being accessed. This cannot be done be a generic data transfer
> function.
>   

   I disagree with your approach of overriding the libata methods at the 
board level, so I suggest to write a new driver. This is too complicated 
stuff for poor old pata_platform. :-)

> Regards,
>
> Graeme

MBR, Sergei