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

[- <a5b6@riseup.net>]

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@riseup.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