Re: [PATCH 1/1] scsi: retrieve cache mode using ATA_16 if normal routine fails

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Hi Sergei,
Thanks for your review comments.

On Sun, Feb 5, 2012 at 5:35 PM, Sergei Shtylyov <sshtylyov@xxxxxxxxxx> wrote:
> Hello.
>
>
> On 03-02-2012 16:59, Amit Sahrawat wrote:
>
>> It has been observed that a number of USB HDD's do not respond correctly
>
>
>   Why are you working around this in libata-scsi.c then if it's USB HDD?
There has been a history to this problem. It has been a long pending
problem with SCSI layer and USB HDD. We observed when we encountered
various Filesystem corruption issues on USB HDD and on analysis - we
found that there is no SYNCHRONIZE_CACHE command going to a number of
USB HDD even though - they do seem to possess WRITE CACHE.
So, drivers/scsi/sd.c - was where we found that WCE is being set for
these kind of devices which will in-turn take care of setting the
correct 'cache_type - Writeback' and also take care of proper working
(by managing correct order in requests queue).
We first did a change by introducing  - mechanism to retrieve cache
bit in sd_read_cache_type, alongwith this we provided an interface
using 'syfs' if we can change the cache type from that place.
But, we received review comments in this regards - that the layer on
which we are doing changes is not the proper place(and also ATA_16
seems to crash some old HDD's, and were advised to look out for
changes in libata-scsi  instead).(Original link -
http://lkml.org/lkml/2011/12/12/164)

So, we went for changes in libata-scsi.

Please let me know in case more information is needed in this regards,
or may be if you could provide more inputs to these sort of changes.
>
>
>> to SCSI mode sense command(retrieve caching pages) which results in their
>> Write Cache being discarded by queue requests i.e., WCE if left set to
>> '0'(disabled).
>> This results in a number of Filesystem corruptions, when the device
>> is unplugged abruptly.
>
>
>> So, in order to identify the devices correctly - give it
>> a last try using ATA_16 after failure from normal routine.
>
>
>   Shouldn't this be done in drivers/usb/storage somewhere?
>
>
>> Signed-off-by: Amit Sahrawat<a.sahrawat@xxxxxxxxxxx>
>> Signed-off-by: Namjae Jeon<namjae.jeon@xxxxxxxxxxx>
>
>
> [...]
>
>
>> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
>> index 508a60b..d5b00e6 100644
>> --- a/drivers/ata/libata-scsi.c
>> +++ b/drivers/ata/libata-scsi.c
>> @@ -562,6 +562,57 @@ error:
>>  }
>>
>>  /**
>> + *      ata_get_cachestatus - Handler for to get WriteCache Status
>> + *                      using ATA_16 scsi command
>> + *      @scsidev: Device to which we are issuing command
>> + *
>> + *      LOCKING:
>> + *      Defined by the SCSI layer.  We don't really care.
>> + *
>> + *      RETURNS:
>> + *      '0' for Write Cache Disabled and on any error.
>> + *      '1' for Write Cache enabled
>> + */
>> +int ata_get_cachestatus(struct scsi_device *scsidev)
>> +{
>> +       int rc = 0;
>> +       u8 scsi_cmd[MAX_COMMAND_SIZE] = {0};
>> +       u8 *sensebuf = NULL, *argbuf = NULL;
>
>
>   No need to initialize them.
Tried to maintain the uniformity in the code for this file, at other
places it is being done like.
>
>
>> +       enum dma_data_direction data_dir;
>> +
>> +       sensebuf = kzalloc(SCSI_SENSE_BUFFERSIZE, GFP_NOIO);
>> +       if (!sensebuf)
>> +               return rc;
>> +
>> +       argbuf = kmalloc(ATA_SECT_SIZE, GFP_KERNEL);
>> +       if (argbuf == NULL)
>
>
>   Could you use an uniform NULL-check, either '!x' or 'x == NULL'?
Agreed, need to stick with one type of comparision.
>
>
>> +               goto error;
>> +
>> +       scsi_cmd[0] = ATA_16;
>> +       scsi_cmd[1]  = (4<<  1); /* PIO Data-in */
>> +       scsi_cmd[2]  = 0x0e;     /* no off.line or cc, read from dev,
>> +                               block count in sector count field */
>> +       data_dir = DMA_FROM_DEVICE;
>> +       scsi_cmd[14] = ATA_IDENTIFY_DEV;
>> +
>> +       if (!scsi_execute(scsidev, scsi_cmd, data_dir, argbuf,
>> ATA_SECT_SIZE,
>> +                               sensebuf, (10*HZ), 5, 0, NULL)) {
>> +               /*
>> +                * '6th' Bit in Word 85 Corresponds to Write Cache
>
>
>   No need for apostrophes here.
Tried to highlight the 6th bit, if this is not the convention, I will
remove this.
>
>> +                * being Enabled/disabled, Word 85 represnets the
>> +                * features supported
>> +                */
>> +               if (le16_to_cpu(((unsigned short *)argbuf)[85])&  0x20)
>>
>> +                       rc = 1;
>> +       }
>> +
>> +error:
>> +       kfree(sensebuf);
>> +       kfree(argbuf);
>> +       return rc;
>> +}
>> +
>> +/**
>>   *    ata_task_ioctl - Handler for HDIO_DRIVE_TASK ioctl
>>   *    @scsidev: Device to which we are issuing command
>>   *    @arg: User provided data for issuing command
>> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
>> index c691fb5..a6b887d 100644
>> --- a/drivers/scsi/sd.c
>> +++ b/drivers/scsi/sd.c
>> @@ -50,6 +50,11 @@
>>  #include<linux/string_helpers.h>
>>  #include<linux/async.h>
>>  #include<linux/slab.h>
>> +
>> +#ifdef CONFIG_ATA
>
>
>   #ifdef not necessary here.
Yes, but just wanted to specifiy for code readability, as there is no
purpose to include - libata header in sd.c
>
>
>> +#include<linux/libata.h>
>> +#endif
>> +
>>  #include<linux/pm_runtime.h>
>>  #include<asm/uaccess.h>
>>  #include<asm/unaligned.h>
>> @@ -2129,7 +2134,11 @@ sd_read_cache_type(struct scsi_disk *sdkp, unsigned
>> char *buffer)
>>                if (modepage == 0x3F) {
>>                        sd_printk(KERN_ERR, sdkp, "No Caching mode page "
>>                                  "present\n");
>> +#ifdef CONFIG_ATA
>> +                       goto WCE_USING_ATA;
>
>
>   Yikes.
>
>
>> +#else
>>                        goto defaults;
>> +#endif
>>                } else if ((buffer[offset]&  0x3f) != modepage) {
>>                        sd_printk(KERN_ERR, sdkp, "Got wrong page\n");
>>                        goto defaults;
>> @@ -2149,6 +2158,14 @@ sd_read_cache_type(struct scsi_disk *sdkp, unsigned
>> char *buffer)
>>                                  "Uses READ/WRITE(6), disabling FUA\n");
>>                        sdkp->DPOFUA = 0;
>>                }
>> +#ifdef CONFIG_ATA
>> +WCE_USING_ATA:
>> +               if (!sdp->removable && !sdkp->WCE) {
>> +                       sd_printk(KERN_NOTICE, sdkp, "Try to check write
>> cache "
>> +                               "enable/disable using ATA command\n");
>> +                       sdkp->WCE = ata_get_cachestatus(sdp);
>> +               }
>> +#endif
>>
>>                if (sdkp->first_scan || old_wce != sdkp->WCE ||
>>                    old_rcd != sdkp->RCD || old_dpofua != sdkp->DPOFUA)
>> diff --git a/include/linux/libata.h b/include/linux/libata.h
>> index cafc09a..33fc73f 100644
>> --- a/include/linux/libata.h
>> +++ b/include/linux/libata.h
>> @@ -84,6 +84,8 @@
>>        }                                                       \
>>  })
>>
>> +#define ATA_IDENTIFY_DEV       0xEC
>> +
>
>
>   This is alerady #defined in <linux/ata.h> as ATA_CMD_ID_ATA.
Yes, will include that instead of redifining.
>
> MBR, Sergei

Please share your inputs to this.

Thanks & Regards,
Amit Sahrawat
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