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V4L/DVB (3766): Correct buffer size calculations in cx88-core.c 

The computation in cx88_risc_buffer suffers from the mistake:
a non-zero padding value can cause more page borders to be crossed,
leading to big buffer over-runs.  
This patch changes the additive constant from 3 + 4 to 4
It also changees the constant in cx88_risc_databuffer from 3 + 4 to 2,
because 2 dwords are the correct vaule.

Signed-off-by: Duncan Sands <baldrick@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>
This commit is contained in:
Duncan Sands 2006-04-11 10:18:57 -03:00 committed by Mauro Carvalho Chehab
parent 9175b8544f
commit bba3ad76a8
1 changed files with 10 additions and 6 deletions
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16
drivers/media/video/cx88/cx88-core.c
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@ -146,9 +146,11 @@ int cx88_risc_buffer(struct pci_dev *pci, struct btcx_riscmem *risc,
fields++;
/* estimate risc mem: worst case is one write per page border +
one write per scan line + syncs + jump (all 2 dwords) */
instructions = (bpl * lines * fields) / PAGE_SIZE + lines * fields;
instructions += 3 + 4;
one write per scan line + syncs + jump (all 2 dwords). Padding
can cause next bpl to start close to a page border. First DMA
region may be smaller than PAGE_SIZE */
instructions = fields * (1 + ((bpl + padding) * lines) / PAGE_SIZE + lines);
instructions += 2;
if ((rc = btcx_riscmem_alloc(pci,risc,instructions*8)) < 0)
return rc;
@ -176,9 +178,11 @@ int cx88_risc_databuffer(struct pci_dev *pci, struct btcx_riscmem *risc,
int rc;
/* estimate risc mem: worst case is one write per page border +
one write per scan line + syncs + jump (all 2 dwords) */
instructions = (bpl * lines) / PAGE_SIZE + lines;
instructions += 3 + 4;
one write per scan line + syncs + jump (all 2 dwords). Here
there is no padding and no sync. First DMA region may be smaller
than PAGE_SIZE */
instructions = 1 + (bpl * lines) / PAGE_SIZE + lines;
instructions += 1;
if ((rc = btcx_riscmem_alloc(pci,risc,instructions*8)) < 0)
return rc;