Re: [PATCH V2 05/13] pm80xx : Support for char device.

[John Garry <john.garry@huawei.com>]

On 12/03/2020 08:49, Jinpu Wang wrote:
> On Wed, Mar 11, 2020 at 11:13 PM Douglas Gilbert <dgilbert@interlog.com> wrote:
>>
>> On 2020-03-11 1:08 p.m., Jinpu Wang wrote:
>>> On Tue, Jan 28, 2020 at 10:43 AM <Deepak.Ukey@microchip.com> wrote:
>>>>
>>>>
>>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>>
>>>> On 22/01/2020 08:50, Deepak.Ukey@microchip.com wrote:
>>>>> -r--r--r-- 1 root root 4096 Jan 21 12:05 running_disparity_error_count
>>>>> ***
>>>>> -r--r--r-- 1 root root 4096 Jan 21 12:05 sas_address
>>>>> lrwxrwxrwx 1 root root    0 Jan 21 11:45 subsystem ->
>>>>> ../../../../../../../class/sas_phy
>>>>> -r--r--r-- 1 root root 4096 Jan 21 12:05 target_port_protocols
>>>>> -rw-r--r-- 1 root root 4096 Jan 21 11:45 uevent
>>>>>
>>>>> Maybe the other stuff provided in the patches are useful, I don't know.
>>>>> But debugfs seems better for that.
>>>>>
>>>>>         - 0006-pm80xx-sysfs-attribute-for-number-of-phys
>>>>>         - 0007-pm80xx-IOCTL-functionality-to-get-phy-status gets things like Programmed Link Rate, Negotiated Link Rate, PHY Identifier
>>>>>         - 0008-pm80xx-IOCTL-functionality-to-get-phy-error provides other things like Invalid Dword Error Count, Disparity Error Count
>>>>>         - Thanks for addressing it. We can get this info from /sys/class/sas_phy and /sys/class/sas_port so we will drop these above mentioned three patches from the next              - patch series.
>>>>>
>>>
>>>>>
>>>>>         - 0009-pm80xx-IOCTL-functionality-for-GPIO
>>>>>         - 0013-pm80xx-IOCTL-functionality-for-TWI-device
>>>>>         - For the above patches management utility passes command specific information to driver through IOCTL structure, which used by driver to frame the command and         - send to FW.  We are using the IOCTL interface for the same. Please let us know your thought.
>>>>
>>>> So I specifically questioned the SGPIO patch and why it would have an IOCTL, as this function is supported in kernel libsas/SAS transport code as an SMP function.
>>>>>    Thank you for your suggestions. We will make use of function supported in libsas.
>>>
>>> So basically you only need IOCTL for GPIO and TWI devices, others can
>>> implement via libsas interface or from sysfs directly.
>>>
>>> I would like to suggest you do send out other changes without the
>>> IOCTL parts first, and consider again Is it really needed by the user
>>> to control GPIO and TWI, and if there is other way to do it?
>>>
>>> Sorry, I don't have a better suggestion!
>>
>> LSI SAS HBAs (LSI now owned by Broadcom) implement an internal ** SMP
>> target. It can be seen here:
>>
>> # ls /dev/bsg
>> 3:0:0:0  3:0:3:0  8:0:0:0  8:0:0:3           end_device-3:1    expander-3:0
>> 3:0:1:0  4:0:0:0  8:0:0:1  8:0:0:4           end_device-3:1:0  expander-3:1
>> 3:0:2:0  7:0:0:0  8:0:0:2  end_device-3:0:1  end_device-3:2    sas_host3
>>
>> It is the last device node: "sas_host3". How do I know it is a SMP target?
>> Because this works:
>>
>> # smp_read_gpio /dev/bsg/sas_host3
>> Read GPIO register response:
>>     GPIO_CFG[0]:
>>       version: 0
>>       GPIO enable: 1
>>       cfg register count: 2
>>       gp register count: 1
>>       supported drive count: 16
>>

JFYI, that specific command is not implemented for libsas SMP host 
handler (see 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/scsi/libsas/sas_host_smp.c?h=v5.6-rc5#n278), 
but the write command should be ok

>> When you work out what LSI are doing with this, perhaps you could write
>> an article about it and make it publicly available.

Firmware magic...

>> It is always a good idea to see how your competitors solve problems :-)
> This sounds indeed a better solution, thanks for the info, Doug
> 
> @Deepak Ukey can you check if you guys can also do it this way?
> 
> Regards,
> Jack Wang
> .
>