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

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Message-ID: <dfb68d3632340c2ddffa487c69723aa3@codeaurora.org>
Date:   Wed, 24 Mar 2021 09:45:45 +0800
From:   Can Guo <cang@...eaurora.org>
To:     Avri Altman <Avri.Altman@....com>
Cc:     daejun7.park@...sung.com, Bean Huo <huobean@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>, 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 20:48, Avri Altman wrote:
>> 
>> 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...
> Looks like this discussion is going the same way as we had in host 
> mode.
> HPB-WRITE-BUFFER 0x2, if exist,  is always a companion to HPB-READ.
> You shouldn't consider them separately.
> 
> The device is expected to handle invalid ppn by itself, and
> specifically for this case,
> As Daejun explained, Handle each HPB-READ (and its companion
> HPB-WRITE-BUFFER) like READ10.
> 
> For device mode, doing nothing in case of dev reset, seems to me like
> the right thing to do.

I just got some feedbacks from other flash vendors, they all commit that
their devices can work well in this scenario [1]. Some of them proposed
even complicated (maybe better) principles of handling the "HPB reset",
but since the device works well in [1], I am OK with current (simpler)
handling of "HPB reset" - in device mode doing nothing, in host mode
re-activate regions that host is trying to do a read to.

Thanks,
Can Guo.

> 
> Thanks,
> Avri
> 
>> 
>> 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.
>> >>>>>>
>> >>>>>>
>> >>>>>>
>> >>>>
>> >>>>
>> >>>>
>> >>
>> >>
>> >>