RE: [RESEND PATCH] scsi: ufs: sysfs: support writing boot_lun attr

[Avri Altman]

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