[Bug 1908450] Re: ide/core.c ATA Major Version reporting incorrect

[Gregory Price]

I would just fix the comment for now, likewise I don't have the time to audit
whether the emulation provides full coverage of the standard.

Really there's two cases here
1) We report ATA4-7 (current status), someone discovers missing bits feature
Response:  They file a ticket on the missing feature.

2) We report ATA3-6 (changed status), legacy stuff checking this bit suddenly 
break
Response:  Rabid screeching somewhere in the depths of the internets.

Fixing the comment is more risk averse and more likely to produce the desirable
outcome (some reads the comment, and discovers a missing ATA feature for the
reported standard).

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https://bugs.launchpad.net/bugs/1908450

Title:
  ide/core.c ATA Major Version reporting incorrect

Status in QEMU:
  New

Bug description:
  @@ -165,7 +165,7 @@ static void ide_identify(IDEState *s)
          put_le16(p + 76, (1 << 8));
      }

      put_le16(p + 80, 0xf0); /* ata3 -> ata6 supported */
  -   put_le16(p + 80, 0xf0); /* ata3 -> ata6 supported */
  +   put_le16(p + 80, ((1 << 6) | (1 << 5) (1 << 4) (1 << 3)); /* ata3 -> ata6 
supported */
      put_le16(p + 81, 0x16); /* conforms to ata5 */
      /* 14=NOP supported, 5=WCACHE supported, 0=SMART supported */
      put_le16(p + 82, (1 << 14) | (1 << 5) | 1);

  
  This field Major Version Number field is presently reporting support for 
ATA-4 through ATA-7.
  Bitfield[80] is defined in the ATA-6 specification below.

  0xF0 = (1<<7) | (1<<6) | (1 << 5) | (1 << 4) // 4-7 - current settings
  0x78 = (1<<6) | (1<<5) | (1 << 4) | (1 << 3) // 3-6 - new settings

  Either the comment is wrong, or the field is wrong. If the field is
  wrong it can cause errors in drivers that check support vs conformity.
  This will not break most guests, since the conformity field is set to
  ATA-5.

  I'm not sure whether this component supports ATA-7, but since it's
  commented as if it supports up through 6, correcting the field
  assignment seems more correct.

  ATA/ATAPI-6 Specification
  
https://web.archive.org/web/20200124094822/https://www.t13.org/Documents/UploadedDocuments/project/d1410r3b-ATA-ATAPI-6.pdf

  Page 116
  80 - M Major version number
  0000h or FFFFh = device does not report version
  F 15 Reserved
  F 14 Reserved for ATA/ATAPI-14
  F 13 Reserved for ATA/ATAPI-13
  F 12 Reserved for ATA/ATAPI-12
  F 11 Reserved for ATA/ATAPI-11
  F 10 Reserved for ATA/ATAPI-10
  F 9 Reserved for ATA/ATAPI-9
  F 8 Reserved for ATA/ATAPI-8
  F 7 Reserved for ATA/ATAPI-7
  F 6 1 = supports ATA/ATAPI-6
  F 5 1 = supports ATA/ATAPI-5
  F 4 1 = supports ATA/ATAPI-4
  F 3 1 = supports ATA-3
  X 2 Obsolete
  X 1 Obsolete
  F 0 Reserved

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