linux-kernel - Re: [PATCH 13/18] ide: use ->tf_load in SELECT

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Date:	Wed, 04 Mar 2009 18:43:45 +0300
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	Sergei Shtylyov <sshtylyov@...mvista.com>
Cc:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/18] ide: use ->tf_load in SELECT_DRIVE()

Hello, I wrote:

>>>>>>>> There should be no functional changes caused by this patch.
>>>>>>>> Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
>>>>>>>> Index: b/drivers/ide/ide-iops.c
>>>>>>>> ===================================================================
>>>>>>>> --- a/drivers/ide/ide-iops.c
>>>>>>>> +++ b/drivers/ide/ide-iops.c
>>>>>>>> @@ -88,11 +88,15 @@ void SELECT_DRIVE (ide_drive_t *drive)
>>>>>>>> {
>>>>>>>>     ide_hwif_t *hwif = drive->hwif;
>>>>>>>>     const struct ide_port_ops *port_ops = hwif->port_ops;
>>>>>>>> +    ide_task_t task;

>>>>>>>>     if (port_ops && port_ops->selectproc)
>>>>>>>>         port_ops->selectproc(drive);
>>>>>>>>
>>>>>>>> -    hwif->OUTB(drive->select.all, hwif->io_ports.device_addr);
>>>>>>>> +    memset(&task, 0, sizeof(task));
>>>>>>>> +    task.tf_flags = IDE_TFLAG_OUT_DEVICE;
>>>>>>>> +
>>>>>>>> +    drive->hwif->tf_load(drive, &task);

>>>>>>>   This actually doesn't seem like a bright idea to me, 
>>>>>>> considering that this gets called when starting every request. 
>>>>>>> How will you look at me adding the transport method for writing 
>>>>>>> this register? :-)

>>>> Please check profiles first -- it might not be worth it. [1]

>>>>>> Convert SELECT_DRIVE() to use ->tf_load instead of ->OUTB.

>>>>>>  OTOH, adding such a "backdoor" to the taskfile doesn't seem very 
>>>>>> consistent... well, I'm not excited about the whole idea 
>>>>>> conversion to tf_{load|read}() -- it's not clear what exactly this 
>>>>>> bought us.

>>>> This was explained some months ago already, so just to recall -- it was
>>>> a part of a bigger work removing duplicated code and allowing 
>>>> abstraction
>>>> of the ATA logic.

>>>> Anyway this is not set in a stone so if you have proposal of a better
>>>> approach please come forward with it.

>>>   Er... I think that the previous IN()/OUT() methods were better. 
>>> Note that we ended up using the local version of them in the dafault 
>>> ide_tf_{load}read}() anyway -- as Alan has pointed out it might be worth 

>> During ide_tf_{load,read}() addition I was a bit too optimistic about
>> the possibility of the quick io{read,write}* conversion later...

>>> splitting those into I/O and memory space versions... although given 
>>> general slowness of the I/O accesses, this is probably not going to 
>>> win much speed-wise.

>> Maybe it would be worth to add ->tf_{inb,outb} to struct ide_tp_ops
>> and convert default tp_ops to use them...  OTOH we should reinvestigate
>> the io{read,write}*() way first (maybe things have improved there)...

>    Yes, let's not be hasty here...

    What I certainly don't like is how tf_load/read() handle LBA48: there's 
much of the code duplication going on. I'll think what can be done about it 
but it may not be easy to tackle... it looks like 'struct ide_taskfile' needs 
to be reorganized to include 2 6-byte sub-structures.

>> Thanks,
>> Bart

MBR, Sergei

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