linux-kernel - Re: [PATCH 1/2] sh: dma: fix `dmaor_read_reg`/`dmaor_write

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Message-ID: <65f873585db0cd9f79a84eb48707413775a9ba5b.camel@physik.fu-berlin.de>
Date:   Sun, 07 May 2023 10:39:17 +0200
From:   John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To:     Artur Rojek <contact@...ur-rojek.eu>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>
Cc:     Rafael Ignacio Zurita <rafaelignacio.zurita@...il.com>,
        linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] sh: dma: fix `dmaor_read_reg`/`dmaor_write_reg`
 macros

On Sat, 2023-05-06 at 16:17 +0200, Artur Rojek wrote:
> Squash two bugs introduced into said macros in 7f47c7189b3e, preventing
> them from proper operation:
> 1) Add DMAOR register offset into the address of the hw reg access,
> 2) Correct a nasty typo in the DMAOR base calculation for
>    `dmaor_write_reg`.
> 
> Signed-off-by: Artur Rojek <contact@...ur-rojek.eu>
> ---
>  arch/sh/drivers/dma/dma-sh.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/sh/drivers/dma/dma-sh.c b/arch/sh/drivers/dma/dma-sh.c
> index 96c626c2cd0a..14c18ebda400 100644
> --- a/arch/sh/drivers/dma/dma-sh.c
> +++ b/arch/sh/drivers/dma/dma-sh.c
> @@ -254,8 +254,11 @@ static int sh_dmac_get_dma_residue(struct dma_channel *chan)
>   * DMAOR bases are broken out amongst channel groups. DMAOR0 manages
>   * channels 0 - 5, DMAOR1 6 - 11 (optional).
>   */
> -#define dmaor_read_reg(n)		__raw_readw(dma_find_base((n)*6))
> -#define dmaor_write_reg(n, data)	__raw_writew(data, dma_find_base(n)*6)
> +#define dmaor_read_reg(n)		__raw_readw(dma_find_base((n) * 6) + \
> +						    DMAOR)
> +#define dmaor_write_reg(n, data)	__raw_writew(data, \
> +						     dma_find_base((n) * 6) + \
> +						     DMAOR)
>  
>  static inline int dmaor_reset(int no)
>  {

I have looked through the changes and the code and I agree that there is a typo
in dmaor_write_regn() that needs to be fixed and that the DMAOR offset is missing
although I don't understand why that didn't break the kernel on other SuperH systems
such as my SH-7785LCR evaluation board or the LANDISK board which Geert uses.

What I also don't understand is the factor 6 the DMA channel number is multiplied
with. When looking at the definition of dma_find_base(), it seems that every channel
equal to 6 or higher will return SH_DMAC_BASE1 as DMA base address. But if we multiply
the parameter with 6, this will apply to every n > 0. Is that correct?

Adrian

-- 
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: :' :  Debian Developer
`. `'   Physicist
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