4.9-stable review patch. If anyone has any objections, please let me know.
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From: Maxime Jayat maxime.jayat@mobile-devices.fr
commit c5637476bbf9bb86c7f0413b8f4822a73d8d2d07 upstream.
Despite the efforts made to correctly read the NDA and CUBC registers, the order in which the registers are read could sometimes lead to an inconsistent state.
Re-using the timeline from the comments, this following timing of registers reads could lead to reading NDA with value "@desc2" and CUBC with value "MAX desc1":
INITD -------- ------------ |____________________| _______________________ _______________ NDA @desc2 / @desc3 _______________________/_______________ __________ ___________ _______________ CUBC 0 / MAX desc1 / MAX desc2 __________/___________/_______________ | | | | Events:(1)(2) (3)(4)
(1) check_nda = @desc2 (2) initd = 1 (3) cur_ubc = MAX desc1 (4) cur_nda = @desc2
This is allowed by the condition ((check_nda == cur_nda) && initd), despite cur_ubc and cur_nda being in the precise state we don't want.
This error leads to incorrect residue computation.
Fix it by inversing the order in which CUBC and INITD are read. This makes sure that NDA and CUBC are always read together either _before_ INITD goes to 0 or _after_ it is back at 1. The case where NDA is read before INITD is at 0 and CUBC is read after INITD is back at 1 will be rejected by check_nda and cur_nda being different.
Fixes: 53398f488821 ("dmaengine: at_xdmac: fix residue corruption") Cc: stable@vger.kernel.org Signed-off-by: Maxime Jayat maxime.jayat@mobile-devices.fr Acked-by: Ludovic Desroches ludovic.desroches@microchip.com Signed-off-by: Vinod Koul vinod.koul@intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/dma/at_xdmac.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/drivers/dma/at_xdmac.c +++ b/drivers/dma/at_xdmac.c @@ -1473,10 +1473,10 @@ at_xdmac_tx_status(struct dma_chan *chan for (retry = 0; retry < AT_XDMAC_RESIDUE_MAX_RETRIES; retry++) { check_nda = at_xdmac_chan_read(atchan, AT_XDMAC_CNDA) & 0xfffffffc; rmb(); - initd = !!(at_xdmac_chan_read(atchan, AT_XDMAC_CC) & AT_XDMAC_CC_INITD); - rmb(); cur_ubc = at_xdmac_chan_read(atchan, AT_XDMAC_CUBC); rmb(); + initd = !!(at_xdmac_chan_read(atchan, AT_XDMAC_CC) & AT_XDMAC_CC_INITD); + rmb(); cur_nda = at_xdmac_chan_read(atchan, AT_XDMAC_CNDA) & 0xfffffffc; rmb();