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SubjectRe: [PATCH v2.6.38-rc7] Revert "libata: ahci_start_engine compliant to AHCI spec"
From
Hi, Tejun,

Defintely. I will clarify it as much as possible and meanwhile, wait
for it to be tested by reporters.

Thanks,
Jian

On Mon, May 23, 2011 at 5:13 AM, Tejun Heo <tj@kernel.org> wrote:
> Hello,
>
> On Fri, May 20, 2011 at 10:02:56AM -0700, Jian Peng wrote:
>> Hi, Tejun/Valdis,
>>
>> Since this is an interoperability issue of SATA host controller, the first
>> step I want to try it to make sure the tweak that MAKE my controller WORK
>> does not break other controllers.
>> You are both right that adding this majic 5ms delay at this place should not
>> be the final solution.
>>
>> If this magic 5ms delay works on other affected systems, I plan to post a
>> new patch that inside ahci_start_engine(), still perform same check, and
>> show warning message if failed, but will set a flag, then still set START
>> bit, and if there is such failure flag, add 5ms delay.
>
> Yeah, sounds like a plan but please add ample comment explaining
> what's going on for which controller including link to the mailing
> list threads.  As we're basically adding a black magic, I would still
> like to enable it only for the affected controllers so that we don't
> have to worry whether there are controllers which are affected by this
> problem but we don't know about.
>
>> --- a/drivers/ata/libahci.c 2011-05-18 14:23:36.564665643 -0700
>> +++ c/drivers/ata/libahci.c 2011-05-20 09:48:06.194663506 -0700
>> @@ -540,6 +540,7 @@
>>   void __iomem *port_mmio = ahci_port_base(ap);
>>   u32 tmp;
>>   u8 status;
>> + int err = 0;
>
> I think
>
>  bool stat_failed = false;
>
> would be more in line with recent coding style.
>
>>   status = readl(port_mmio + PORT_TFDATA) & 0xFF;
>>
>> @@ -553,12 +554,12 @@
>>    * specific controller will fail under this condition
>>    */
>>   if (status & (ATA_BUSY | ATA_DRQ))
>> -  return;
>> +  err = 1;
>>   else {
>>    ahci_scr_read(&ap->link, SCR_STATUS, &tmp);
>>
>>    if ((tmp & 0xf) != 0x3)
>> -   return;
>> +   err = 1;
>>   }
>>
>>   /* start DMA */
>> @@ -566,6 +567,13 @@
>>   tmp |= PORT_CMD_START;
>>   writel(tmp, port_mmio + PORT_CMD);
>>   readl(port_mmio + PORT_CMD); /* flush */
>> +
>> + /* Some controllers need longer time to be ready */
>> + if(err) {
>> +  printk(KERN_WARNING
>> +   "Controller in wrong state when setting START bit\n");
>> +  msleep(5);
>
>  ata_port_printk()?
>
> Thanks.
>
> --
> tejun
>
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