On Tue, Oct 11, 2011 at 7:49 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxx>
>>
>> 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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