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Date: Fri, 27 May 2022 13:50:02 +0100
From: Caleb Connolly <caleb.connolly@...aro.org>
To: Avri Altman <Avri.Altman@....com>,
"a5b6@...eup.net" <a5b6@...eup.net>,
Alim Akhtar <alim.akhtar@...sung.com>,
"James E . J . Bottomley" <jejb@...ux.ibm.com>,
"Martin K . Petersen" <martin.petersen@...cle.com>,
"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc: "~postmarketos/upstreaming@...ts.sr.ht"
<~postmarketos/upstreaming@...ts.sr.ht>,
"phone-devel@...r.kernel.org" <phone-devel@...r.kernel.org>
Subject: Re: RE: [RESEND PATCH] scsi: ufs: sysfs: support writing boot_lun
attr
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@...eup.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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