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?
>
> > Signed-off-by: Nia Espera <a5b6@xxxxxxxxxx>
> > ---
> >   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