Hi James, Few queries relating to solution for this long pending problem. As per your suggestions - it is clear - we cannot have this as part of default routine to retrieve WCE using ATA - as for some USB HDD - it will result in halting their operations. So, 1) USB quirks -> i think this will only be a workaround for few USB hard disks - wherein we can their add their entries in the quirks list and control this WC. So, this wont be a solution which can be used as part of a long term solution. 2) As part of 'sysfs' interface - there is already an array for cache_types in sd.c - Can we make an entry in this array for "write back(ata cmd)" and make corresponding changes - to reflect this when we do " echo "write back(ata cmd) > /sys/class/scsi_disk/<>/cache_type". So, these changes won't be part of default routine - but this will still need minor changes in sd.c - will those changes be acceptable? sd_store_cache_type()->revalidate_disk()->sd_revalidate_disk()->sd_read_cache_type() Please share your opinion to bring out a solution to this. Thanks & Regards, Amit Sahrawat On Thu, Feb 16, 2012 at 6:58 PM, James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote: > On Thu, 2012-02-16 at 12:22 +0530, Amit Sahrawat wrote: > >> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c >> index c691fb5..3ca507a 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 >> +#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; >> +#else >> goto defaults; >> +#endif >> } else if ((buffer[offset] & 0x3f) != modepage) { >> sd_printk(KERN_ERR, sdkp, "Got wrong page\n"); >> goto defaults; >> @@ -2149,6 +2158,15 @@ 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 >> + > > I already said before, this is a non starter: we can't randomly send > SCSI encapsulated ATA commands to disks from sd. What we can do is give > you a WCE variable you can change on the fly in sysfs via whatever > mechanism is most appropriate (but this would have to be a mechanism > external to sd.c). > > Alternatively, you can co-opt the USB quirks handling to set it for you. > > James > > -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html