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SubjectRe: [Patch] SCSI: Retrieve Cache Mode Using SG_ATA_16 if normal routine fails
From
On Tue, Oct 11, 2011 at 7:49 PM, Alan Stern <stern@rowland.harvard.edu> wrote:
> On Tue, 11 Oct 2011, Amit Sahrawat wrote:
>
>> SCSI: Retrieve Cache Mode Using SG_ATA_16 if normal routine fails
>>
>> It has been observed that a number of USB HDD's do not respond correctly
>> 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). So, in order to identify the devices correctly - give it
>> a last try using SG_ATA_16 after failure from normal routine.
>>
>> Signed-off-by: Amit Sahrawat <amit.sahrawat83@gmail.com>
>>
>> diff -Nurp linux-Orig/drivers/scsi/sd.c linux-Updated/drivers/scsi/sd.c
>> --- linux-Orig/drivers/scsi/sd.c      2011-10-11 11:02:48.000000000 +0530
>> +++ linux-Updated/drivers/scsi/sd.c   2011-10-11 11:10:09.000000000 +0530
>> @@ -56,6 +56,7 @@
>>  #include <asm/uaccess.h>
>>  #include <asm/unaligned.h>
>>
>> +#include <scsi/sg.h>
>>  #include <scsi/scsi.h>
>>  #include <scsi/scsi_cmnd.h>
>>  #include <scsi/scsi_dbg.h>
>> @@ -134,6 +135,58 @@ static const char *sd_cache_types[] = {
>>       "write back, no read (daft)"
>>  };
>>
>> +/* Relevant Structure and Function to be used to Retrieve
>> + * Caching Information from USB HDD - this is picked from
>> + * source code of 'hdparm'
>> + *
>> + *
>> + * Definitions and structures for use with SG_IO + ATA_16:
>> + * */
>> +#define SG_ATA_16               0x85
>> +#define SG_ATA_16_LEN           16
>> +
>> +#define ATA_OP_IDENTIFY              0xec
>> +
>> +/*
>> + * Some useful ATA register bits
>> + */
>> +enum {
>> +        ATA_USING_LBA           = (1 << 6),
>> +        ATA_STAT_DRQ            = (1 << 3),
>> +        ATA_STAT_ERR            = (1 << 0),
>> +};
>> +
>> +struct ata_lba_regs {
>> +        __u8    feat;
>> +        __u8    nsect;
>> +        __u8    lbal;
>> +        __u8    lbam;
>> +        __u8    lbah;
>> +};
>> +struct ata_tf {
>> +        __u8                    dev;
>> +        __u8                    command;
>> +        __u8                    error;
>> +        __u8                    status;
>> +        __u8                    is_lba48;
>> +        struct ata_lba_regs     lob;
>> +        struct ata_lba_regs     hob;
>> +};
>
> Don't these things already exist in some standard header file?  If not,
> shouldn't they be added in a more central location?
>
>> +__u64 tf_to_lba (struct ata_tf *tf)
>> +{
>> +        __u32 lba24, lbah;
>> +        __u64 lba64;
>> +
>> +        lba24 = (tf->lob.lbah << 16) | (tf->lob.lbam << 8) | (tf->lob.lbal);
>> +        if (tf->is_lba48)
>> +                lbah = (tf->hob.lbah << 16) | (tf->hob.lbam << 8) |
>> (tf->hob.lbal);
>> +        else
>> +                lbah = (tf->dev & 0x0f);
>> +        lba64 = (((__u64)lbah) << 24) | (__u64)lba24;
>> +        return lba64;
>> +}
>> +
>>  static ssize_t
>>  sd_store_cache_type(struct device *dev, struct device_attribute *attr,
>>                   const char *buf, size_t count)
>> @@ -1839,6 +1892,18 @@ sd_read_cache_type(struct scsi_disk *sdk
>>       int old_rcd = sdkp->RCD;
>>       int old_dpofua = sdkp->DPOFUA;
>>
>> +     struct ata_tf tf;
>> +     struct sg_io_hdr io_hdr;
>> +     unsigned char cdb[SG_ATA_16_LEN] = {0};
>> +     unsigned char sb[32] = {0};
>> +     unsigned char buf[512] = {0};
>
> Arrays generally should not have static initializers.  Also, a 512-byte
> array is too large to allocate on the stack.  And there's already a
> 512-byte array available -- it's named "buffer".
>
>> +     unsigned short wce_word = 0;
>
> There's no reason to initialize this variable.
>
>> +     void *data_cmd = buf;
>
> Why do you need to alias a perfectly good variable?
>
>> +
>> +     memset(cdb, 0, SG_ATA_16_LEN);
>> +     memset(&tf, 0, sizeof(struct ata_tf));
>> +     memset(&io_hdr, 0, sizeof(struct sg_io_hdr));
>
> There's no point initializing these things before you know that they
> will be used.
>
>> +
>>         first_len = 4;
>>         if (sdp->skip_ms_page_8) {
>>                 if (sdp->type == TYPE_RBC)
>> @@ -1961,7 +2026,6 @@ Page_found:
>>                                 sdkp->DPOFUA ? "supports DPO and FUA"
>>                                 : "doesn't support DPO or FUA");
>>
>> -             return;
>>       }
>>
>>  bad_sense:
>> @@ -1974,8 +2038,64 @@ bad_sense:
>>               sd_printk(KERN_ERR, sdkp, "Asking for cache data failed\n");
>>
>>  defaults:
>> -     sd_printk(KERN_ERR, sdkp, "Assuming drive cache: write through\n");
>> -     sdkp->WCE = 0;
>> +     if (sdkp->WCE)
>> +             return;
>> +     else {
>> +             sd_printk(KERN_ERR, sdkp, "Normal Routine Failed: Trying ATA_16\n");
>
> Instead of adding an awful lot of code inside an "else" clause, it
> would be better to put this into its own subroutine.
>
>> +
>> +             /* The below are necessary parameters which are to set - in order
>> +             to make use of ATA_OP_IDENTIFY command */
>> +             tf.lob.lbal = 0;
>> +             tf.lob.lbam = 0;
>> +             tf.lob.lbah = 0;
>> +             tf.lob.nsect = 1; //Number of Sectors to Read
>> +             tf.lob.feat = 0;
>> +
>> +             /* Command Descriptor Block For SCSI    */
>> +             cdb[0] = SG_ATA_16;
>> +             cdb[1] = 0x08;
>> +             cdb[2] = 0x0e;
>> +             cdb[6] = 0x01; //No. of Sectors To Read
>> +             cdb[13] = ATA_USING_LBA;
>> +             cdb[14] = ATA_OP_IDENTIFY;
>> +
>> +             io_hdr.cmd_len = SG_ATA_16_LEN;
>> +             io_hdr.interface_id = SG_INTERFACE_ID_ORIG;
>> +             io_hdr.mx_sb_len= sizeof(sb);
>> +             io_hdr.dxfer_direction = SG_DXFER_FROM_DEV;
>> +             io_hdr.dxfer_len = sizeof(buf);
>> +             io_hdr.dxferp = data_cmd;
>> +             io_hdr.cmdp = cdb;
>> +             io_hdr.sbp = sb;
>> +             io_hdr.pack_id = tf_to_lba(&tf);
>> +             io_hdr.timeout = 0;
>> +
>> +             if (!scsi_cmd_ioctl(sdkp->disk->queue, sdkp->disk,
>> O_RDONLY|O_NONBLOCK, SG_IO, &io_hdr))
>
> Do you really need to do an ioctl?  Why not call scsi_execute_req()
> directly?
>
>> +             {
>> +#if 0
>> +#define DUMP_BYTES_BUFFER(x...) printk( x )
>> +                     int i;
>> +                     for (i = 0; i < 32; i++)
>> +                             DUMP_BYTES_BUFFER(" %02x", sb[i]);
>> +                     DUMP_BYTES_BUFFER("\n");
>> +                     for (i = 0; i < 512; i++)
>> +                             DUMP_BYTES_BUFFER(" %02x", buf[i]);
>> +                     DUMP_BYTES_BUFFER("\n");
>> +                     printk(KERN_ERR"82 - [0x%x], 85 -
>> [0x%x]\n",((unsigned short*)data_cmd)[82],((unsigned
>> short*)data_cmd)[85]);
>> +#endif
>
> For the final patch submission, of course this section should be
> removed.
>
>> +                     /* '6th' Bit in Word 85 Corresponds to Write Cache being Enabled/disabled*/
>> +                     wce_word = le16_to_cpu(((unsigned short*)data_cmd)[85]);
>> +                     if (wce_word & 0x20) {
>> +                             sdkp->WCE = 1;
>> +                             sd_printk(KERN_NOTICE, sdkp, "Write Cache Enabled
>> after ATA_16 response\n");
>> +                     } else
>> +                             goto write_through;
>> +             } else {
>> +write_through:
>> +                     sd_printk(KERN_ERR, sdkp, "Assuming drive cache: write through\n");
>> +                     sdkp->WCE = 0;
>> +             }
>> +     }
>>       sdkp->RCD = 0;
>>       sdkp->DPOFUA = 0;
>>  }
>
> Besides the potential problems raised by other people, these structural
> weaknesses in the patch should be fixed.
>
> Alan Stern
>
>

Thanks Alan for the thorough review, I will consider all your points.
Also, will try and make use of scsi_execute_req() instead of ioctl().

Regards,
Amit Sahrawat
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