>
> 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@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
