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

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Date:   Wed, 6 Apr 2022 11:24:09 +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 4/5/22 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.

> +		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