Re: [PATCH v4 4/8] dmaengine: mmp_pdma: Add operations structure for controller abstraction

[Guodong Xu <guodong@riscstar.com>]

Hi, Dan

On Mon, Aug 18, 2025 at 3:17 PM Dan Carpenter <dan.carpenter@linaro.org> wrote:
>
> Hi Guodong,
>
> kernel test robot noticed the following build warnings:
>
> url:    https://github.com/intel-lab-lkp/linux/commits/Guodong-Xu/dt-bindings-dma-Add-SpacemiT-K1-PDMA-controller/20250815-132049
> base:   062b3e4a1f880f104a8d4b90b767788786aa7b78
> patch link:    https://lore.kernel.org/r/20250815-working_dma_0701_v2-v4-4-62145ab6ea30%40riscstar.com
> patch subject: [PATCH v4 4/8] dmaengine: mmp_pdma: Add operations structure for controller abstraction
> config: parisc-randconfig-r072-20250818 (https://download.01.org/0day-ci/archive/20250818/202508181040.az8RxLrG-lkp@intel.com/config)
> compiler: hppa-linux-gcc (GCC) 8.5.0
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
> | Closes: https://lore.kernel.org/r/202508181040.az8RxLrG-lkp@intel.com/
>
> smatch warnings:
> drivers/dma/mmp_pdma.c:546 mmp_pdma_prep_memcpy() warn: variable dereferenced before check 'dchan' (see line 542)
> drivers/dma/mmp_pdma.c:712 mmp_pdma_prep_dma_cyclic() warn: variable dereferenced before check 'dchan' (see line 708)
>
> vim +/dchan +546 drivers/dma/mmp_pdma.c
>
> c8acd6aa6bed3c Zhangfei Gao     2012-09-03  536  static struct dma_async_tx_descriptor *
> c8acd6aa6bed3c Zhangfei Gao     2012-09-03  537  mmp_pdma_prep_memcpy(struct dma_chan *dchan,
> c8acd6aa6bed3c Zhangfei Gao     2012-09-03  538                      dma_addr_t dma_dst, dma_addr_t dma_src,
> c8acd6aa6bed3c Zhangfei Gao     2012-09-03  539                      size_t len, unsigned long flags)
> c8acd6aa6bed3c Zhangfei Gao     2012-09-03  540  {
> c8acd6aa6bed3c Zhangfei Gao     2012-09-03  541         struct mmp_pdma_chan *chan;
> 918da7ee50b22b Guodong Xu       2025-08-15 @542         struct mmp_pdma_device *pdev = to_mmp_pdma_dev(dchan->device);
>                                                                                                        ^^^^^^^^^^^^^
> The patch adds a new dereference
>
> c8acd6aa6bed3c Zhangfei Gao     2012-09-03  543         struct mmp_pdma_desc_sw *first = NULL, *prev = NULL, *new;
> c8acd6aa6bed3c Zhangfei Gao     2012-09-03  544         size_t copy = 0;
> c8acd6aa6bed3c Zhangfei Gao     2012-09-03  545
> c8acd6aa6bed3c Zhangfei Gao     2012-09-03 @546         if (!dchan)
>                                                             ^^^^^^
> But the old existing code assumed dchan could be NULL
>

Thank you for the report and findings.
This and the next one, they are bugs, and I will
fix them in the next version.

BR,
Guodong

> c8acd6aa6bed3c Zhangfei Gao     2012-09-03  547                 return NULL;
> c8acd6aa6bed3c Zhangfei Gao     2012-09-03  548
> c8acd6aa6bed3c Zhangfei Gao     2012-09-03  549         if (!len)
> c8acd6aa6bed3c Zhangfei Gao     2012-09-03  550                 return NULL;
> c8acd6aa6bed3c Zhangfei Gao     2012-09-03  551
> c8acd6aa6bed3c Zhangfei Gao     2012-09-03  552         chan = to_mmp_pdma_chan(dchan);
>
> [ snip ]
>
> 2b7f65b11d87f9 Joe Perches      2013-11-17  701  static struct dma_async_tx_descriptor *
> 2b7f65b11d87f9 Joe Perches      2013-11-17  702  mmp_pdma_prep_dma_cyclic(struct dma_chan *dchan,
> 2b7f65b11d87f9 Joe Perches      2013-11-17  703                          dma_addr_t buf_addr, size_t len, size_t period_len,
> 2b7f65b11d87f9 Joe Perches      2013-11-17  704                          enum dma_transfer_direction direction,
> 31c1e5a1350ae8 Laurent Pinchart 2014-08-01  705                          unsigned long flags)
> 50440d74aae318 Daniel Mack      2013-08-21  706  {
> 50440d74aae318 Daniel Mack      2013-08-21  707         struct mmp_pdma_chan *chan;
> 918da7ee50b22b Guodong Xu       2025-08-15 @708         struct mmp_pdma_device *pdev = to_mmp_pdma_dev(dchan->device);
>                                                                                                        ^^^^^^^^^^^^^
>
>
> 50440d74aae318 Daniel Mack      2013-08-21  709         struct mmp_pdma_desc_sw *first = NULL, *prev = NULL, *new;
> 50440d74aae318 Daniel Mack      2013-08-21  710         dma_addr_t dma_src, dma_dst;
> 50440d74aae318 Daniel Mack      2013-08-21  711
> 50440d74aae318 Daniel Mack      2013-08-21 @712         if (!dchan || !len || !period_len)
>                                                             ^^^^^^
> Same.
>
>
> 50440d74aae318 Daniel Mack      2013-08-21  713                 return NULL;
> 50440d74aae318 Daniel Mack      2013-08-21  714
> 50440d74aae318 Daniel Mack      2013-08-21  715         /* the buffer length must be a multiple of period_len */
>
> --
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>