linux-kernel - Re: [PATCH] spi: spi_amd: Add HIDDMA basic write support

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Message-ID: <CAMuHMdX_ugjS475udqa1oOOfbOJ+0s_JAKcCyCcdQfPhhaWOTQ@mail.gmail.com>
Date: Mon, 12 May 2025 20:34:52 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: "Rangoju, Raju" <raju.rangoju@....com>
Cc: kernel test robot <lkp@...el.com>, broonie@...nel.org, oe-kbuild-all@...ts.linux.dev, 
	linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Krishnamoorthi M <krishnamoorthi.m@....com>, 
	Akshata MukundShetty <akshata.mukundshetty@....com>
Subject: Re: [PATCH] spi: spi_amd: Add HIDDMA basic write support

Hi Raju,

On Mon, 12 May 2025 at 19:55, Rangoju, Raju <raju.rangoju@....com> wrote:
> On 5/12/2025 7:47 PM, Geert Uytterhoeven wrote:
> > On Mon, 12 May 2025 at 09:29, Rangoju, Raju <raju.rangoju@....com> wrote:
> >> On 5/11/2025 3:51 AM, kernel test robot wrote:
> >>> kernel test robot noticed the following build warnings:
> >>>
> >>> [auto build test WARNING on v6.15-rc5]
> >>> [also build test WARNING on linus/master]
> >>> [cannot apply to broonie-spi/for-next next-20250509]
> >>> [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/Raju-Rangoju/spi-spi_amd-Add-HIDDMA-basic-write-support/20250510-021954
> >>> base:   v6.15-rc5
> >>> patch link:    https://lore.kernel.org/r/20250509181737.997167-1-Raju.Rangoju%40amd.com
> >>> patch subject: [PATCH] spi: spi_amd: Add HIDDMA basic write support
> >>> config: m68k-randconfig-r111-20250511 (https://download.01.org/0day-ci/archive/20250511/202505110641.zLT16Dv7-lkp@intel.com/config)
> >>> compiler: m68k-linux-gcc (GCC) 14.2.0
> >>
> >> Thanks for reporting this. We do not support m68k.
> >
> > All write[bwlq]() functions take a volatile void __iomem pointer
> > (https://elixir.bootlin.com/linux/v6.14.6/source/include/asm-generic/io.h#L174)
> > while you are passing a void *, so sparse should complain about this
> > on all architectures.
>
> My bad, with the following flags included, sparse now complains this on
> all architectures.
>
> -fmax-errors=unlimited -fmax-warnings=unlimited
>
> And sparse is right, this driver is using MMIO
> > accessors on allocated DMA memory, which is just plain wrong:
> >
> >      amd_spi->dma_virt_addr = dma_alloc_coherent(dev, AMD_SPI_HID2_DMA_SIZE,
> >              &amd_spi->phy_dma_buf, GFP_KERNEL);
> >
> >       for (i = 0; left_data >= 8; i++, left_data -= 8)
> >              *buf_64++ = readq((u8 __iomem *)amd_spi->dma_virt_addr + (i * 8));
> >
> >> Will re-spin v2 with necessary changes in Kconfig.
> >
> > Please fix the real issue instead ;-)
>
> We are using read*/write* calls instead of memcpy to copy data to/from
> DMA memory due to performance concerns, as we observed better throughput
> during continuous read/write compared to the memcpy functions.

Perhaps your memcpy() copies backwards?
https://lwn.net/Articles/1016300/

There is no guarantee that read*/write* calls work on normal RAM on
all architectures. It may just crash, as some architectures return
cookies instead of real pointers when mapping MMIO.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds