Re: [PATCH] libata: Disable ATA_CMD_READ_LOG_DMA_EXT in problematic cases.

[Damien Le Moal <Damien.LeMoal@wdc.com>]

On 2021/08/16 1:27, Reimar Döffinger wrote:
> The ATA_CMD_READ_LOG_DMA_EXT can cause controller/device to
> become unresponsive until the next power cycle.
> This seems to particularly affect IDE to SATA adapters,
> possibly in combination with certain SATA SSDs, though
> there might be more/different cases.
> Comment 5 of https://bugzilla.kernel.org/show_bug.cgi?id=195895
> is an example.
> Disable it by default on Crucial MX500 devices and all
> PATA controllers.
> Also add an option to set the workaround state, which might
> help with gathering more data on the exact devices/controllers
> affected, and speed up narrowing down the cause for users that
> are affect but not covered by the added quirks.
> Existing workarounds like forcing PIO mode do not work
> (in addition to the performance issues) because READ_LOG_DMA
> is issued even if PIO mode is forced.
> 
> Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  2 ++
>  drivers/ata/libata-core.c                       | 15 +++++++++++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index bdb22006f713..191502e8fa74 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2551,6 +2551,8 @@
>  
>  			* [no]ncqtrim: Turn off queued DSM TRIM.
>  
> +			* [no]dmalog: Turn off use of ATA_CMD_READ_LOG_DMA_EXT (0x47) command
> +
>  			* nohrst, nosrst, norst: suppress hard, soft
>  			  and both resets.
>  
> diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
> index 61c762961ca8..219fa92ffc06 100644
> --- a/drivers/ata/libata-core.c
> +++ b/drivers/ata/libata-core.c
> @@ -2004,7 +2004,11 @@ unsigned int ata_read_log_page(struct ata_device *dev, u8 log,
>  
>  retry:
>  	ata_tf_init(dev, &tf);
> +	/* Do not even attempt DMA with PATA-SATA adapters, they seem likely to
> +	 * hang, see https://bugzilla.kernel.org/show_bug.cgi?id=195895
> +	 */

This is not the standard kernel comment style. Multi-lines comment should start
with a "/*" line:

+	/*
+	 * Do not even attempt DMA with PATA-SATA adapters, they seem likely to
+	 * hang, see https://bugzilla.kernel.org/show_bug.cgi?id=195895
+	 */

Also, I would remove the bugzilla reference since it is in the commit message.

>  	if (dev->dma_mode && ata_id_has_read_log_dma_ext(dev->id) &&
> +	    (ap_flags & ATA_FLAG_SATA) &&

Why is this necessary since you have the ATA_HORKAGE_NO_DMA_LOG flag ?
If this is really necessary, ATA_HORKAGE_NO_DMA_LOG should be set for all
devices that have ATA_FLAG_SATA when the device is initialized. With that, this
additional condition can go away.

>  	    !(dev->horkage & ATA_HORKAGE_NO_DMA_LOG)) {
>  		tf.command = ATA_CMD_READ_LOG_DMA_EXT;
>  		tf.protocol = ATA_PROT_DMA;
> @@ -4000,6 +4004,15 @@ static const struct ata_blacklist_entry ata_device_blacklist [] = {
>  	{ "WDC WD3000JD-*",		NULL,	ATA_HORKAGE_WD_BROKEN_LPM },
>  	{ "WDC WD3200JD-*",		NULL,	ATA_HORKAGE_WD_BROKEN_LPM },
>  
> +	/* Devices with observed READ LOG DMA issues - unclear if only
> +	 * specific firmware versions or only in combination with specific
> +	 * controllers.
> +	 * Specifically broken combinations reported
> +	 * CT1000MX500SSD4, M3CR020 with B350M-Mortar
> +	 * CT500MX500SSD4, M3CR023 with PATA-SATA adapter
> +	 * https://bugzilla.kernel.org/show_bug.cgi?id=195895
> +	 */

Same comment about the comment format.
I would also remove the bugzilla reference as it is in the commit message.

> +	{ "Crucial_CT*MX500*",		NULL,	ATA_HORKAGE_NO_DMA_LOG },
>  	/* End Marker */
>  	{ }
>  };
> @@ -6104,6 +6117,8 @@ static int __init ata_parse_force_one(char **cur,
>  		{ "ncq",	.horkage_off	= ATA_HORKAGE_NONCQ },
>  		{ "noncqtrim",	.horkage_on	= ATA_HORKAGE_NO_NCQ_TRIM },
>  		{ "ncqtrim",	.horkage_off	= ATA_HORKAGE_NO_NCQ_TRIM },
> +		{ "nodmalog",	.horkage_on	= ATA_HORKAGE_NO_DMA_LOG },
> +		{ "dmalog",	.horkage_off	= ATA_HORKAGE_NO_DMA_LOG },
>  		{ "dump_id",	.horkage_on	= ATA_HORKAGE_DUMP_ID },
>  		{ "pio0",	.xfer_mask	= 1 << (ATA_SHIFT_PIO + 0) },
>  		{ "pio1",	.xfer_mask	= 1 << (ATA_SHIFT_PIO + 1) },
> 


-- 
Damien Le Moal
Western Digital Research