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

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Message-ID: <20210323063726epcms2p28aadb16bb96943ade1d2b288bb634811@epcms2p2>
Date:   Tue, 23 Mar 2021 15:37:26 +0900
From:   Daejun Park <daejun7.park@...sung.com>
To:     Can Guo <cang@...eaurora.org>,
        Daejun Park <daejun7.park@...sung.com>
CC:     Bean Huo <huobean@...il.com>, Greg KH <gregkh@...uxfoundation.org>,
        "avri.altman@....com" <avri.altman@....com>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "asutoshd@...eaurora.org" <asutoshd@...eaurora.org>,
        "stanley.chu@...iatek.com" <stanley.chu@...iatek.com>,
        "bvanassche@....org" <bvanassche@....org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...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: Re: [PATCH v31 2/4] scsi: ufs: L2P map management for HPB read

>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.

Thanks,
Daejun

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