Messages in this thread | | | Date | Fri, 27 May 2022 13:50:02 +0100 | Subject | Re: RE: [RESEND PATCH] scsi: ufs: sysfs: support writing boot_lun attr | From | Caleb Connolly <> |
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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
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