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

[Caleb Connolly <caleb.connolly@linaro.org>]

On 27/05/2022 07:17, Avri Altman wrote:
>>
>> 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.
Hi Avri,

Could you explain why the NAK here? Boot LUN switching is used on a lot 
of embedded devices to implement A/B updates, Android devices are just 
one such example.

Distributions like postmarketOS [1] aim to support upstream Linux on 
mobile devices, particularly those that are no longer supported by the 
vendor. Being able to make use of features like A/B updates is something 
that I expect more distributions to be considering in the future, as we 
start to see more Linux devices with support for features like this.

If safety is a concern, or if the values are device specific, we can 
look at protecting the write functionality and configuration behind DT 
properties, or coming up with another alternative.

[1]: https://postmarketos.org

Kind regards,
Caleb (they/he)

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