Re: EP93xx PIO IDE driver proposal

["João Ramos" <joao.ramos@inov.pt>]

João Ramos escreveu:
>
>>
>> Yes! :)
>>
>> There is still a room for improvement though -- it would be better to 
>> fix
>> IDE core to set PIO0 before probing devices for all host controllers.
>>
>> Moreover it seems that doing it this way would allow us to remove 
>> ->init_hwif
>> method from this driver and do all necessary setup in ep93xx_ide_probe()
>> (this controller is a single port one so theoretically there 
>> shouldn't be
>> a need for having per-port ->init_hwif implementation).
>>   
>
> So after all this discussion ;-) , my driver will have no 'init_hwif' 
> method, and the setup code will be on 'ep93xx_ide_probe', which will 
> configure entirely the IDE host controller.
> Moreover, this initial configuration will setup the controller to work 
> at PIO Mode 0. Later on, the 'set_pio_mode' method will be called and 
> the controller will configure itself according to the PIO mode 
> reported by the IDE core.
>
> Can I proceed this way?
>
>>  
>>> There's just only one issue; normally, I would setup the specific 
>>> timings (t0, t1, t2, t2i, etc) in the 'pio_set_mode' hook. However, 
>>> if you look further in the driver, those timings aren't defined 
>>> through a memory controller but instead manually enforced by 
>>> 'ndelay' calls (arghhh).
>>> This means that in my low-level procedures for reading and writing, 
>>> I need to have access to the timings (or the struct ide_timing) 
>>> corresponding to the PIO mode selected, in order to use the correct 
>>> delays.
>>>
>>> My question is: which is the best way to accomplish this? Declaring 
>>> a global struct ide_timing variable pointer that always holds the 
>>> correct ide_timing struct to the selected PIO mode? Or should I 
>>> always check (in some manner) what is the current PIO mode and then 
>>> select the adequate delays?
>>>     
>>
>> I think that the setting variable pointer in ->set_pio_mode method would
>> work best.  Seems like the existing drive_data field of ide_drive_t 
>> is well
>> suited for this purpose (however it may be worth to convert it to 
>> 'void *'
>> type while we are it).
>>  

Are you sure I can do this safely?

Using the patch i've sent earlier, I am using the 'drive_data' field  
(now converted to void * type) to store the struct ide_timing pointer 
that holds the adequate timings for the selected PIO mode.
This is working, and the fix you suggested works, but sometimes I get a 
null pointer dereference I can't seem to figure why.
As I needed to define low-level read/write procedures, I've defined the 
entire ide_tp_ops structure with my own provided methods.
For the tf_load, tf_read, input_data and output_data methods, the fix is 
easy since I have an ide_drive_t structure pointer as a parameter, so I 
access the timing structure using:

struct ide_timing *t = (struct ide_timing *) ide_get_drivedata(drive);

However, for the remaining methods (exec_command, read_status, 
read_altstatus, write_devctl and dev_select), I only have access to an 
ide_hwif_t pointer, so in order to get access to the containing 
ide_drive_t and then to the struct ide_timing pointer stored before, I do:

ide_drive_t *drive = (ide_drive_t *) container_of(&hwif, ide_drive_t, hwif);
struct ide_timing *t = (struct ide_timing *) ide_get_drivedata(drive);

And this seems to work, however at some point, after a while I get a 
kernel Oops pointing out a null pointer dereference.

Can someone help me here?
Is there a better way to retrieve the ide_drive_t pointer from the 
ide_hwif_t structure?

Best regards,
João Ramos

-- 
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    João Ramos        <joao.ramos@inov.pt>

    INOV INESC Inovação - ESTG Leiria
    Escola Superior de Tecnologia e Gestão de Leiria
    Edíficio C1, Campus 2
    Morro do Lena, Alto do Vieiro
    Leiria
    2411-901 Leiria
    Portugal

    Tel: +351244843424
    Fax: +351244843424

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