PRD_ENTRIES is 256

PRD_ENTRIES is 256

[William Lee Irwin III]

PRD_ENTRIES is specified to be precisely 256; on platforms where
PAGE_SIZE varies from 4KB the calculation in the current expression
defining it is inaccurate, which may cause crashes. This patch changes
it to the constant literal 256.


-- wli


===== include/linux/ide.h 1.88 vs edited =====
--- 1.88/include/linux/ide.h	Tue Feb 10 07:35:39 2004
+++ edited/include/linux/ide.h	Wed Feb 25 01:46:45 2004
@@ -224,7 +224,7 @@
  * allowing each to have about 256 entries (8 bytes each) from this.
  */
 #define PRD_BYTES       8
-#define PRD_ENTRIES     (PAGE_SIZE / (2 * PRD_BYTES))
+#define PRD_ENTRIES     256
 
 /*
  * Some more useful definitions

Re: PRD_ENTRIES is 256

[Bartlomiej Zolnierkiewicz]

On Wednesday 25 of February 2004 10:53, William Lee Irwin III wrote:
> PRD_ENTRIES is specified to be precisely 256; on platforms where
> PAGE_SIZE varies from 4KB the calculation in the current expression
> defining it is inaccurate, which may cause crashes. This patch changes
> it to the constant literal 256.

Ok, thanks.  However I cannot find 256 entries limit in any ATA document
and from looking at the code 512 entries shouldn't be a problem (?).

--bart

> -- wli
>
>
> ===== include/linux/ide.h 1.88 vs edited =====
> --- 1.88/include/linux/ide.h	Tue Feb 10 07:35:39 2004
> +++ edited/include/linux/ide.h	Wed Feb 25 01:46:45 2004
> @@ -224,7 +224,7 @@
>   * allowing each to have about 256 entries (8 bytes each) from this.
>   */
>  #define PRD_BYTES       8
> -#define PRD_ENTRIES     (PAGE_SIZE / (2 * PRD_BYTES))
> +#define PRD_ENTRIES     256
>
>  /*
>   * Some more useful definitions

Re: PRD_ENTRIES is 256

[William Lee Irwin III]

On Wednesday 25 of February 2004 10:53, William Lee Irwin III wrote:
>> PRD_ENTRIES is specified to be precisely 256; on platforms where
>> PAGE_SIZE varies from 4KB the calculation in the current expression
>> defining it is inaccurate, which may cause crashes. This patch changes
>> it to the constant literal 256.

On Wed, Feb 25, 2004 at 02:11:13PM +0100, Bartlomiej Zolnierkiewicz wrote:
> Ok, thanks.  However I cannot find 256 entries limit in any ATA document
> and from looking at the code 512 entries shouldn't be a problem (?).
> --bart

The numbers I'm fishing out of things say that the PRD table can't
exceed 64KB in size as it can't cross a 64KB boundary and its length
is specified as a 16-bit byte count, so some other method of sizing
the thing may be in order. I do recall something went wrong at the
time I ran into this. If I turn up where I thought the number 256 came
from I'll cite it.


-- wli

Re: PRD_ENTRIES is 256

[Jeff Garzik]

Bartlomiej Zolnierkiewicz wrote:
> On Wednesday 25 of February 2004 10:53, William Lee Irwin III wrote:
> 
>>PRD_ENTRIES is specified to be precisely 256; on platforms where
>>PAGE_SIZE varies from 4KB the calculation in the current expression
>>defining it is inaccurate, which may cause crashes. This patch changes
>>it to the constant literal 256.
> 
> 
> Ok, thanks.  However I cannot find 256 entries limit in any ATA document
> and from looking at the code 512 entries shouldn't be a problem (?).


I can't find the 256 limit either, but I would swear it exists...  I'll 
ask around.  Certainly it would be nice for lba48 to have larger tables...

	Jeff