Re: [PATCH v4 12/23] ata: libahci: Extend port-cmd flags set with port capabilities

Damien Le Moal
2022-06-18T06:52:42Z

On 6/18/22 05:31, Serge Semin wrote:
> On Thu, Jun 16, 2022 at 09:28:18AM +0900, Damien Le Moal wrote:
>> On 2022/06/16 5:58, Serge Semin wrote:
>>> On Tue, Jun 14, 2022 at 05:32:41PM +0900, Damien Le Moal wrote:
>>>> On 6/10/22 17:17, Serge Semin wrote:
>>>>> Currently not all of the Port-specific capabilities listed in the
>>>>
>>>> s/listed/are listed
>>>>
>>>>> PORT_CMD-enumeration. Let's extend that set with the Cold Presence
>>>>> Detection and Mechanical Presence Switch attached to the Port flags [1] so
>>>>> to closeup the set of the platform-specific port-capabilities flags. Note
>>>>> these flags are supposed to be set by the platform firmware if there is
>>>>> one. Alternatively as we are about to do they can be set by means of the
>>>>> OF properties.
>>>>>
>>>>> While at it replace PORT_IRQ_DEV_ILCK with PORT_IRQ_DMPS and fix the
>>>>> comment there. In accordance with [2] that IRQ flag is supposed to
>>>>> indicate the state of the signal coming from the Mechanical Presence
>>>>> Switch.
>>>>>
>>>>> [1] Serial ATA AHCI 1.3.1 Specification, p.27
>>>>> [2] Serial ATA AHCI 1.3.1 Specification, p.24, p.88
>>>>>
>>>>> Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
>>>>> Reviewed-by: Hannes Reinecke <hare@suse.de>
>>>>>
>>>>> ---
>>>>>
>>>>> Changelog v4:
>>>>> - Fix the DMPS macros name in the patch log. (@Sergei Shtylyov)
>>>>> ---
>>>>> drivers/ata/ahci.h | 7 ++++++-
>>>>> 1 file changed, 6 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/ata/ahci.h b/drivers/ata/ahci.h
>>>>> index 7d834deefeb9..f501531bd1b3 100644
>>>>> --- a/drivers/ata/ahci.h
>>>>> +++ b/drivers/ata/ahci.h
>>>>> @@ -138,7 +138,7 @@ enum {
>>>>> PORT_IRQ_BAD_PMP = (1 << 23), /* incorrect port multiplier */
>>>>>
>>>>> PORT_IRQ_PHYRDY = (1 << 22), /* PhyRdy changed */
>>>>> - PORT_IRQ_DEV_ILCK = (1 << 7), /* device interlock */
>>>>> + PORT_IRQ_DMPS = (1 << 7), /* mechanical presence status */
>>>>> PORT_IRQ_CONNECT = (1 << 6), /* port connect change status */
>>>>> PORT_IRQ_SG_DONE = (1 << 5), /* descriptor processed */
>>>>> PORT_IRQ_UNK_FIS = (1 << 4), /* unknown FIS rx'd */
>>>>> @@ -166,6 +166,8 @@ enum {
>>>>> PORT_CMD_ATAPI = (1 << 24), /* Device is ATAPI */
>>>>> PORT_CMD_FBSCP = (1 << 22), /* FBS Capable Port */
>>>>> PORT_CMD_ESP = (1 << 21), /* External Sata Port */
>>>>> + PORT_CMD_CPD = (1 << 20), /* Cold Presence Detection */
>>>>> + PORT_CMD_MPSP = (1 << 19), /* Mechanical Presence Switch */
>>>>> PORT_CMD_HPCP = (1 << 18), /* HotPlug Capable Port */
>>>>> PORT_CMD_PMP = (1 << 17), /* PMP attached */
>>>>> PORT_CMD_LIST_ON = (1 << 15), /* cmd list DMA engine running */
>>>>> @@ -181,6 +183,9 @@ enum {
>>>>> PORT_CMD_ICC_PARTIAL = (0x2 << 28), /* Put i/f in partial state */
>>>>> PORT_CMD_ICC_SLUMBER = (0x6 << 28), /* Put i/f in slumber state */
>>>>>
>>>>> + PORT_CMD_CAP = PORT_CMD_HPCP | PORT_CMD_MPSP |
>>>>> + PORT_CMD_CPD | PORT_CMD_ESP | PORT_CMD_FBSCP,
>>>>
>>>
>>>> What is this one for ? A comment above it would be nice.
>>>
>>> Isn't it obviously inferrable from the definition and the item name?
>>
>
>> I am guessing from the name. Am I guessing OK ? A comment would still be nice.
>> Why just these bits ? There are more cap/support indicator bits in that port cmd
>> bitfield. So why this particular set of bits ? What do they mean all together ?
>
> Normally the variable/constant name should be self-content (as the
> kernel coding style doc states and what the common sense suggests). So
> the reader could correctly guess its purpose/content/value. In this
> case PORT_CMD_CAP - means PORT CMD capabilities mask. All of the
> possible flags have been set in that mask. There are no more
> capabilities in the PORT CMD register left undeclared. That's why the
> name is selected the way it is and why I haven't added any comment in
> here (what the kernel coding style says about the over-commenting the
> code).

Yes, I understood from the name what it is. What I do NOT understand is
why all the feature bits are not there. Why this subset only ? A comment
about that would be nice so that the reason for it is not lost.

>
>>
>> Sure I can go and read the specs to figure it out. But again, a comment would
>> avoid readers of the code to have to decrypt all that.
>
> If you still insist on having an additional comment. I can add
> something like "/* PORT_CMD capabilities mask */". Are you ok with it?

That does not help on its own. The macro name says that already. I would
like a note about why only these features are selected.

>
> -Sergey
>
>>
>>>
>>> -Sergey
>>>
>>>>
>>>>> +
>>>>> /* PORT_FBS bits */
>>>>> PORT_FBS_DWE_OFFSET = 16, /* FBS device with error offset */
>>>>> PORT_FBS_ADO_OFFSET = 12, /* FBS active dev optimization offset */
>>>>
>>>>
>>>> --
>>>> Damien Le Moal
>>>> Western Digital Research
>>
>>
>> --
>> Damien Le Moal
>> Western Digital Research

--
Damien Le Moal
Western Digital Research