Re: [PATCH v8 2/2] drm: add kms driver for loongson display controller

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HI,

On 2023/3/28 17:27, kernel test robot wrote:
Hi Sui,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on drm-misc/drm-misc-next]
[also build test WARNING on linus/master v6.3-rc4 next-20230328]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Sui-Jingfeng/MAINTAINERS-add-maintainers-for-DRM-LOONGSON-driver/20230320-180408
base:   git://anongit.freedesktop.org/drm/drm-misc drm-misc-next
patch link:    https://lore.kernel.org/r/20230320100131.1277034-3-15330273260%40189.cn
patch subject: [PATCH v8 2/2] drm: add kms driver for loongson display controller
config: i386-allyesconfig (https://download.01.org/0day-ci/archive/20230328/202303281754.jWI20j2C-lkp@xxxxxxxxx/config)
compiler: clang version 14.0.6 (https://github.com/llvm/llvm-project f28c006a5895fc0e329fe15fead81e37457cb1d1)
reproduce (this is a W=1 build):
         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
         chmod +x ~/bin/make.cross
         # https://github.com/intel-lab-lkp/linux/commit/80b4115f44993f4ebf47b1cb9e8f02953575b977
         git remote add linux-review https://github.com/intel-lab-lkp/linux
         git fetch --no-tags linux-review Sui-Jingfeng/MAINTAINERS-add-maintainers-for-DRM-LOONGSON-driver/20230320-180408
         git checkout 80b4115f44993f4ebf47b1cb9e8f02953575b977
         # save the config file
         mkdir build_dir && cp config build_dir/.config
         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=i386 olddefconfig
         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=i386 SHELL=/bin/bash drivers/accel/ drivers/gpu/drm/loongson/ drivers/iio/light/ drivers/media/pci/intel/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@xxxxxxxxx>
| Link: https://lore.kernel.org/oe-kbuild-all/202303281754.jWI20j2C-lkp@xxxxxxxxx/

All warnings (new ones prefixed by >>):

drivers/gpu/drm/loongson/lsdc_drv.c:232:11: warning: variable 'gpu' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
            else if (descp->chip == CHIP_LS7A2000)
                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
    drivers/gpu/drm/loongson/lsdc_drv.c:235:7: note: uninitialized use occurs here
            if (!gpu) {
                 ^~~
    drivers/gpu/drm/loongson/lsdc_drv.c:232:7: note: remove the 'if' if its condition is always true
            else if (descp->chip == CHIP_LS7A2000)
                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    drivers/gpu/drm/loongson/lsdc_drv.c:217:21: note: initialize the variable 'gpu' to silence this warning
            struct pci_dev *gpu;
                               ^
                                = NULL
    1 warning generated.
--

In practice,  either  descp->chip == CHIP_LS7A2000 or descp->chip == CHIP_LS7A1000 will be happened at runtime.

the variable 'gpu' is guaranteed to be initialized when code run at  drivers/gpu/drm/loongson/lsdc_drv.c:235

This warnning is almost wrong here.

drivers/gpu/drm/loongson/lsdc_pll.c:188:14: warning: variable 'diff' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
                                    else if (clock_khz < computed)
                                             ^~~~~~~~~~~~~~~~~~~~
    drivers/gpu/drm/loongson/lsdc_pll.c:191:9: note: uninitialized use occurs here
                                    if (diff < min) {
                                        ^~~~
    drivers/gpu/drm/loongson/lsdc_pll.c:188:10: note: remove the 'if' if its condition is always true
                                    else if (clock_khz < computed)
                                         ^~~~~~~~~~~~~~~~~~~~~~~~~
    drivers/gpu/drm/loongson/lsdc_pll.c:177:22: note: initialize the variable 'diff' to silence this warning
                                    unsigned int diff;
                                                     ^
                                                      = 0
    1 warning generated.

Here the robot is also wrong here in practice,

because either  if (clock_khz >= computed) or else if (clock_khz < computed) will be happen.

'diff' variable is guaranteed to be initialized.


vim +232 drivers/gpu/drm/loongson/lsdc_drv.c

    212	
    213	static int lsdc_get_dedicated_vram(struct lsdc_device *ldev,
    214					   const struct lsdc_desc *descp)
    215	{
    216		struct drm_device *ddev = &ldev->base;
    217		struct pci_dev *gpu;
    218		resource_size_t base, size;
    219	
    220		/*
    221		 * The GPU and display controller in LS7A1000/LS7A2000 are separated
    222		 * PCIE devices, they are two devices not one. The DC does not has a
    223		 * dedicate VRAM bar, because the BIOS engineer choose to assign the
    224		 * VRAM to the GPU device. Sadly, after years application, this form
    225		 * as a convention for loongson integrated graphics. Bar 2 of the GPU
    226		 * device contain the base address and size of the VRAM, both the GPU
    227		 * and the DC can access the on-board VRAM as long as the DMA address
    228		 * emitted fall in [base, base + size).
    229		 */
    230		if (descp->chip == CHIP_LS7A1000)
    231			gpu = pci_get_device(PCI_VENDOR_ID_LOONGSON, 0x7A15, NULL);
  > 232		else if (descp->chip == CHIP_LS7A2000)
    233			gpu = pci_get_device(PCI_VENDOR_ID_LOONGSON, 0x7A25, NULL);
    234	
    235		if (!gpu) {
    236			drm_warn(ddev, "No GPU device found\n");
    237			return -ENODEV;
    238		}
    239	
    240		base = pci_resource_start(gpu, 2);
    241		size = pci_resource_len(gpu, 2);
    242	
    243		ldev->vram_base = base;
    244		ldev->vram_size = size;
    245	
    246		drm_info(ddev, "dedicated vram start: 0x%llx, size: %uMB\n",
    247			 (u64)base, (u32)(size >> 20));
    248	
    249		return 0;
    250	}
    251	




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