lib/zlib: DFLTCC support inflate with small window

There is no hardware control for DFLTCC window size.  After this change,
software and hardware window formats no longer match: the software will
use wbits and wsize, and the hardware will use HB_BITS and HB_SIZE.

Since neither dictionary manipulation nor internal allocation functions
are relevant to kernel zlib and zlib_inflate_workspacesize() always use
MAX_WBITS for window size calculation, only dfltcc_can_inflate() and
dfltcc_inflate() functions are affected by this patch.

This commit is based on:
  zlib-ng/zlib-ng@3eab317

Link: https://lkml.kernel.org/r/20230126131428.1222214-8-zaslonko@linux.ibm.com
Signed-off-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: mzaslonk

lib/zlib_dfltcc/dfltcc_inflate.c

@@ -22,10 +22,6 @@ int dfltcc_can_inflate(
             zlib_dfltcc_support == ZLIB_DFLTCC_DEFLATE_ONLY)
         return 0;
 
-    /* Unsupported compression settings */
-    if (state->wbits != HB_BITS)
-        return 0;
-
     /* Unsupported hardware */
     return is_bit_set(dfltcc_state->af.fns, DFLTCC_XPND) &&
                is_bit_set(dfltcc_state->af.fmts, DFLTCC_FMT0);
@@ -129,8 +125,6 @@ dfltcc_inflate_action dfltcc_inflate(
     /* Translate stream to parameter block */
     param->cvt = CVT_ADLER32;
     param->sbb = state->bits;
-    param->hl = state->whave; /* Software and hardware history formats match */
-    param->ho = (state->write - state->whave) & ((1 << HB_BITS) - 1);
     if (param->hl)
         param->nt = 0; /* Honor history for the first block */
     param->cv = state->check;
@@ -144,8 +138,6 @@ dfltcc_inflate_action dfltcc_inflate(
     strm->msg = oesc_msg(dfltcc_state->msg, param->oesc);
     state->last = cc == DFLTCC_CC_OK;
     state->bits = param->sbb;
-    state->whave = param->hl;
-    state->write = (param->ho + param->hl) & ((1 << HB_BITS) - 1);
     state->check = param->cv;
     if (cc == DFLTCC_CC_OP2_CORRUPT && param->oesc != 0) {
         /* Report an error if stream is corrupted */