linux-kernel - RE: [RESEND PATCH] scsi: ufs: sysfs: support writing boot

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Date:   Fri, 27 May 2022 06:17:57 +0000
From:   Avri Altman <Avri.Altman@....com>
To:     "a5b6@...eup.net" <a5b6@...eup.net>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        "James E . J . Bottomley" <jejb@...ux.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "~postmarketos/upstreaming@...ts.sr.ht" 
        <~postmarketos/upstreaming@...ts.sr.ht>,
        "phone-devel@...r.kernel.org" <phone-devel@...r.kernel.org>
Subject: RE: [RESEND PATCH] scsi: ufs: sysfs: support writing boot_lun attr

> 
> Hi,
> 
> My usecase is enabling boot slot switching on Android A/B devices, where the
> active LUN has to be changed in order to facilitate e.g. dual-booting Android
> and mainline Linux. A similar interface is exposed by Android, albeit via ioctl. I've
> tested this patch and confirmed it enabled the necessary functionality.
> 
> On 25/05/2022 21:34, Avri Altman wrote:
> > Hi,
> >> Expands sysfs boot_lun attribute to be writable. Necessary to enable
> >> proper support for LUN switching on some UFS devices.
> > Can you please elaborate why is it necessary?
> > What use case are you running?
NAK with prejudice.

Thanks,
Avri

> >
> >> Signed-off-by: Nia Espera <a5b6@...eup.net>
> >> ---
> >>   drivers/scsi/ufs/ufs-sysfs.c | 67 +++++++++++++++++++++++++++++++++++-
> >>   1 file changed, 66 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/scsi/ufs/ufs-sysfs.c
> >> b/drivers/scsi/ufs/ufs-sysfs.c index 5c405ff7b6ea..7bf5d6c3d0ec
> >> 100644
> >> --- a/drivers/scsi/ufs/ufs-sysfs.c
> >> +++ b/drivers/scsi/ufs/ufs-sysfs.c
> >> @@ -1047,6 +1047,71 @@ static inline bool ufshcd_is_wb_attrs(enum
> >> attr_idn
> >> idn)
> >>                  idn <= QUERY_ATTR_IDN_CURR_WB_BUFF_SIZE;
> >>   }
> >>
> >> +static ssize_t boot_lun_enabled_show(struct device *dev,
> >> +                                    struct device_attribute *attr,
> >> +char *buf) {
> >> +       struct ufs_hba *hba = dev_get_drvdata(dev);
> >> +       u32 slot;
> >> +       int ret;
> >> +       u8 index = 0;
> >> +
> >> +       down(&hba->host_sem);
> >> +       if (!ufshcd_is_user_access_allowed(hba)) {
> >> +               up(&hba->host_sem);
> >> +               return -EBUSY;
> >> +       }
> >> +       if (ufshcd_is_wb_attrs(QUERY_ATTR_IDN_BOOT_LU_EN))
> > Clearly bBootLunEn is not a WB attribute.
> >
> >> +               index = ufshcd_wb_get_query_index(hba);
> >> +       ufshcd_rpm_get_sync(hba);
> >> +
> >> +       ret = ufshcd_query_attr(hba, UPIU_QUERY_OPCODE_READ_ATTR,
> >> +               QUERY_ATTR_IDN_BOOT_LU_EN, index, 0, &slot);
> >> +
> >> +       ufshcd_rpm_put_sync(hba);
> >> +       if (ret) {
> >> +               ret = -EINVAL;
> >> +               goto out;
> >> +       }
> >> +
> >> +       ret = sysfs_emit(buf, "0x%08X\n", slot);
> >> +out:
> >> +       up(&hba->host_sem);
> >> +       return ret;
> >> +}
> >> +
> >> +static ssize_t boot_lun_enabled_store(struct device *dev,
> >> +                                     struct device_attribute *attr,
> >> +                                     const char *buf, size_t count)
> >> +{
> >> +       struct ufs_hba *hba = dev_get_drvdata(dev);
> >> +       u32 slot;
> >> +       int ret;
> >> +       u8 index = 0;
> >> +
> >> +       if (kstrtouint(buf, 0, &slot) < 0)
> >> +               return -EINVAL;
> > You need to verify that no one set bBootLunEn = 0x0 because the device won't
> boot.
> > Better check explicitly that slot != bBootLunEn and its either 1 or 2.
> >
> > Thanks,
> > Avri
> >
> >> +
> >> +       down(&hba->host_sem);
> >> +       if (!ufshcd_is_user_access_allowed(hba)) {
> >> +               up(&hba->host_sem);
> >> +               return -EBUSY;
> >> +       }
> >> +       if (ufshcd_is_wb_attrs(QUERY_ATTR_IDN_BOOT_LU_EN))
> >> +               index = ufshcd_wb_get_query_index(hba);
> >> +       ufshcd_rpm_get_sync(hba);
> >> +
> >> +       ret = ufshcd_query_attr_retry(hba,
> UPIU_QUERY_OPCODE_WRITE_ATTR,
> >> +                                     QUERY_ATTR_IDN_BOOT_LU_EN, index, 0, &slot);
> >> +       ufshcd_rpm_put_sync(hba);
> >> +       if (ret) {
> >> +               ret = -EINVAL;
> >> +               goto out;
> >> +       }
> >> +out:
> >> +       up(&hba->host_sem);
> >> +       return ret ? ret : count;
> >> +}
> >> +
> >>   #define UFS_ATTRIBUTE(_name, _uname)                                   \
> >>   static ssize_t _name##_show(struct device *dev,                                \
> >>          struct device_attribute *attr, char *buf)                       \
> >> @@ -1077,8 +1142,8 @@ out:                                                                      \
> >>          return ret;                                                     \
> >>   }                                                                      \
> >>   static DEVICE_ATTR_RO(_name)
> >> +static DEVICE_ATTR_RW(boot_lun_enabled);
> >>
> >> -UFS_ATTRIBUTE(boot_lun_enabled, _BOOT_LU_EN);
> >>   UFS_ATTRIBUTE(max_data_size_hpb_single_cmd,
> _MAX_HPB_SINGLE_CMD);
> >>   UFS_ATTRIBUTE(current_power_mode, _POWER_MODE);
> >>   UFS_ATTRIBUTE(active_icc_level, _ACTIVE_ICC_LVL);
> >> --
> >> 2.36.1