linux-kernel - Re: [PATCH v31 2/4] scsi: ufs: L2P map management for HPB read

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Date:   Tue, 23 Mar 2021 14:47:32 +0800
From:   Can Guo <cang@...eaurora.org>
To:     daejun7.park@...sung.com
Cc:     Bean Huo <huobean@...il.com>, Greg KH <gregkh@...uxfoundation.org>,
        avri.altman@....com, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, asutoshd@...eaurora.org,
        stanley.chu@...iatek.com, bvanassche@....org,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        ALIM AKHTAR <alim.akhtar@...sung.com>,
        JinHwan Park <jh.i.park@...sung.com>,
        Javier Gonzalez <javier.gonz@...sung.com>,
        Sung-Jun Park <sungjun07.park@...sung.com>,
        Jinyoung CHOI <j-young.choi@...sung.com>,
        Dukhyun Kwon <d_hyun.kwon@...sung.com>,
        Keoseong Park <keosung.park@...sung.com>,
        Jaemyung Lee <jaemyung.lee@...sung.com>,
        Jieon Seol <jieon.seol@...sung.com>
Subject: Re: [PATCH v31 2/4] scsi: ufs: L2P map management for HPB read

On 2021-03-23 14:37, Daejun Park wrote:
>> On 2021-03-23 14:19, Daejun Park wrote:
>>>> On 2021-03-23 13:37, Daejun Park wrote:
>>>>>> On 2021-03-23 12:22, Can Guo wrote:
>>>>>>> On 2021-03-22 17:11, Bean Huo wrote:
>>>>>>>> On Mon, 2021-03-22 at 15:54 +0900, Daejun Park wrote:
>>>>>>>>> +       switch (rsp_field->hpb_op) {
>>>>>>>>> 
>>>>>>>>> +       case HPB_RSP_REQ_REGION_UPDATE:
>>>>>>>>> 
>>>>>>>>> +               if (data_seg_len != DEV_DATA_SEG_LEN)
>>>>>>>>> 
>>>>>>>>> +                       dev_warn(&hpb->sdev_ufs_lu->sdev_dev,
>>>>>>>>> 
>>>>>>>>> +                                "%s: data seg length is not
>>>>>>>>> same.\n",
>>>>>>>>> 
>>>>>>>>> +                                __func__);
>>>>>>>>> 
>>>>>>>>> +               ufshpb_rsp_req_region_update(hpb, rsp_field);
>>>>>>>>> 
>>>>>>>>> +               break;
>>>>>>>>> 
>>>>>>>>> +       case HPB_RSP_DEV_RESET:
>>>>>>>>> 
>>>>>>>>> +               dev_warn(&hpb->sdev_ufs_lu->sdev_dev,
>>>>>>>>> 
>>>>>>>>> +                        "UFS device lost HPB information 
>>>>>>>>> during
>>>>>>>>> PM.\n");
>>>>>>>>> 
>>>>>>>>> +               break;
>>>>>>>> 
>>>>>>>> Hi Deajun,
>>>>>>>> This series looks good to me. Just here I have one question. You
>>>>>>>> didn't
>>>>>>>> handle HPB_RSP_DEV_RESET, just a warning.  Based on your SS UFS,
>>>>>>>> how
>>>>>>>> to
>>>>>>>> handle HPB_RSP_DEV_RESET from the host side? Do you think we 
>>>>>>>> shoud
>>>>>>>> reset host side HPB entry as well or what else?
>>>>>>>> 
>>>>>>>> 
>>>>>>>> Bean
>>>>>>> 
>>>>>>> Same question here - I am still collecting feedbacks from flash
>>>>>>> vendors
>>>>>>> about
>>>>>>> what is recommanded host behavior on reception of HPB Op code 
>>>>>>> 0x2,
>>>>>>> since it
>>>>>>> is not cleared defined in HPB2.0 specs.
>>>>>>> 
>>>>>>> Can Guo.
>>>>>> 
>>>>>> I think the question should be asked in the HPB2.0 patch, since in
>>>>>> HPB1.0 device
>>>>>> control mode, a HPB reset in device side does not impact anything 
>>>>>> in
>>>>>> host side -
>>>>>> host is not writing back any HPB entries to device anyways and HPB
>>>>>> Read
>>>>>> cmd with
>>>>>> invalid HPB entries shall be treated as normal Read(10) cmd 
>>>>>> without
>>>>>> any
>>>>>> problems.
>>>>> 
>>>>> Yes, UFS device will process read command even the HPB entries are
>>>>> valid or
>>>>> not. So it is warning about read performance drop by dev reset.
>>>> 
>>>> Yeah, but still I am 100% sure about what should host do in case of
>>>> HPB2.0
>>>> when it receives HPB Op code 0x2, I am waiting for feedbacks.
>>> 
>>> I think the host has two choices when it receives 0x2.
>>> One is nothing on host.
>>> The other is discarding all HPB entries in the host.
>>> 
>>> In the JEDEC HPB spec, it as follows:
>>> When the device is powered off by the host, the device may restore 
>>> L2P
>>> map
>>> data upon power up or build from the host’s HPB READ command.
>>> 
>>> If some UFS builds L2P map data from the host's HPB READ commands, we
>>> don't
>>> have to discard HPB entries in the host.
>>> 
>>> So I thinks there is nothing to do when it receives 0x2.
>> 
>> But in HPB2.0, if we do nothing to active regions in host side, host 
>> can
>> write
>> HPB entries (which host thinks valid, but actually invalid in device
>> side since
>> reset happened) back to device through HPB Write Buffer cmds (BUFFER 
>> ID
>> = 0x2).
>> My question is that are all UFSs OK with this?
> 
> Yes, it must be OK.
> 
> Please refer the following the HPB 2.0 spec:
> 
> If the HPB Entries sent by HPB WRITE BUFFER are removed by the device,
> for example, because they are not consumed for a long enough period of 
> time,
> then the HPB READ command for the removed HPB entries shall be handled 
> as a
> normal READ command.
> 

No, it is talking about the subsequent HPB READ cmd sent after a HPB 
WRITE BUFFER cmd,
but not the HPB WRITE BUFFER cmd itself...

Thanks,
Can Guo.

> Thanks,
> Daejun
> 
>> Thanks,
>> Can Guo.
>> 
>>> 
>>> Thanks,
>>> Daejun
>>> 
>>>> Thanks,
>>>> Can Guo.
>>>> 
>>>>> 
>>>>> Thanks,
>>>>> Daejun
>>>>> 
>>>>>> Please correct me if I am wrong.
>>>>> 
>>>>> 
>>>>> 
>>>>>> Thanks,
>>>>>> Can Guo.
>>>>>> 
>>>>>> 
>>>>>> 
>>>> 
>>>> 
>>>> 
>> 
>> 
>>