linux-kernel - Re: [PATCH v3 2/2] ata: ahci: Protect users from setting policies their drives don't support

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Message-ID: <0548f45e-5ab6-c905-2d49-ab52fbf4c098@opensource.wdc.com>
Date:   Wed, 6 Apr 2022 13:38:50 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     Mario Limonciello <mario.limonciello@....com>
Cc:     "open list:LIBATA SUBSYSTEM (Serial and Parallel ATA drivers)" 
        <linux-ide@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>, hdegoede@...hat.com
Subject: Re: [PATCH v3 2/2] ata: ahci: Protect users from setting policies
 their drives don't support

On 4/6/22 11:24, Damien Le Moal wrote:
> On 4/5/22 04:45, Mario Limonciello wrote:
>> As the default low power policy applies to more chipsets and drives, it's
>> important to make sure that drives actually support the policy that a 
>> user
>> selected in their kernel configuration.
>>
>> If the drive doesn't support slumber, don't let the default policy for 
>> the
>> ATA port be `min_power` or `min_power_with_partial`.
>>
>> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
>> ---
>> v2->v3:
>>   * Fix typo
>>   * Try to reset to CONFIG_SATA_LPM_POLICY unless that's too aggressive
>>     then take MED_POWER.
>>   drivers/ata/libata-sata.c | 12 ++++++++++++
>>   1 file changed, 12 insertions(+)
>>
>> diff --git a/drivers/ata/libata-sata.c b/drivers/ata/libata-sata.c
>> index 044a16daa2d4..b41de7e03dce 100644
>> --- a/drivers/ata/libata-sata.c
>> +++ b/drivers/ata/libata-sata.c
>> @@ -13,6 +13,7 @@
>>   #include <scsi/scsi_device.h>
>>   #include <linux/libata.h>
>> +#include "ahci.h"
>>   #include "libata.h"
>>   #include "libata-transport.h"
>> @@ -368,10 +369,21 @@ int sata_link_scr_lpm(struct ata_link *link, 
>> enum ata_lpm_policy policy,
>>                 bool spm_wakeup)
>>   {
>>       struct ata_eh_context *ehc = &link->eh_context;
>> +    struct ata_port *ap = link->ap;
>> +    struct ahci_host_priv *hpriv;
> 
> That does not work. This function is used by the ata_piix driver too, 
> which is not ahci...
> 
>>       bool woken_up = false;
>>       u32 scontrol;
>>       int rc;
>> +    hpriv = ap->host->private_data;
>> +    if (policy >= ATA_LPM_MIN_POWER_WITH_PARTIAL &&
>> +      !(hpriv->cap & HOST_CAP_SSC)) {
> 
> ...which mean that this flag needs to be moved to struct ata_host to 
> keep this function generic for different LLDDs.

Here I meant having a ata_host flag equivalent, indicating the adapter 
supports slumber state.

> 
>> +        policy = (CONFIG_SATA_LPM_POLICY < 
>> ATA_LPM_MIN_POWER_WITH_PARTIAL) ?
>> +             CONFIG_SATA_LPM_POLICY : ATA_LPM_MED_POWER;
> 
> I really prefer an explicit "if () else" for readability.
> Also, please revert here to CONFIG_SATA_MOBILE_LPM_POLICY.
> 
>> +        dev_warn(ap->host->dev,
>> +            "This drive doesn't support slumber; resetting policy to 
>> %d\n", policy);
> 
> s/doesn't/does not
> 
>> +    }
>> +
>>       rc = sata_scr_read(link, SCR_CONTROL, &scontrol);
>>       if (rc)
>>           return rc;
> 
> Also, as patch 3 of this series, can you add the patch that changes 
> CONFIG_SATA_MOBILE_LPM_POLICY to being "3" by default ?
> 
> And please use a cover letter when you have more than 1 patch. The 
> change log can then be in the cover letter instead of in each patch.
> 


-- 
Damien Le Moal
Western Digital Research