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Date: Sat, 13 May 2023 13:41:54 +0200
From: Artur Rojek <contact@...ur-rojek.eu>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
Yoshinori Sato <ysato@...rs.sourceforge.jp>,
Rich Felker <dalias@...c.org>,
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 2023-05-08 13:20, Geert Uytterhoeven wrote:
> Hi Artur,
>
> On Sun, May 7, 2023 at 11:43 AM Artur Rojek <contact@...ur-rojek.eu>
> wrote:
>> On 2023-05-07 10:39, John Paul Adrian Glaubitz wrote:
>> > 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>\
>
> Thanks for your patch!
>
>> >> --- 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)
>
> Fixes: 7f47c7189b3e8f19 ("sh: dma: More legacy cpu dma chainsawing.")
> Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
>
>> >> 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.
>>
>> I also wondered that. On SH7709 it's a hard panic, it should be the
>> same
>> elsewhere.
>
> Landisk does not seem to use DMA.
> I did have CONFIG_SH_DMA=n, but enabling it does not make any
> difference.
>
>> > 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?
>>
>> As confusing as they look, those macros take dmaor index (a number in
>> range 0 <= n < NR_DMAOR) as parameter, then multiply it by 6 to
>> convert
>> it to a format compatible with `dma_find_base` (which expects a
>> channel
>> index). In practice `n` will be either 0 or 1, so dma_find_base(0 * 6)
>> will return SH_DMAC_BASE0, while dma_find_base(1 * 6) SH_DMAC_BASE1.
>
> Looks like this is still broken on e.g. SH7751R, which has 8 channels,
> both handled by a single DMAOR register at offset 0x40...
>
> While e.g. dma_base_addr() seems to have some provision for this
> (cfr. the "chan >= 9" (not "8") check), dma_find_base() will fail, as
> arch/sh/include/cpu-sh4/cpu/dma.h defines SH_DMAC_BASE1.
Yikes!
If this series hasn't been merged yet, perhaps we could fix this issue
in v2. I have something like this in mind (untested):
```
diff --git a/arch/sh/drivers/dma/dma-sh.c b/arch/sh/drivers/dma/dma-sh.c
index 14c18ebda400..306fba1564e5 100644
--- a/arch/sh/drivers/dma/dma-sh.c
+++ b/arch/sh/drivers/dma/dma-sh.c
@@ -18,6 +18,18 @@
#include <cpu/dma-register.h>
#include <cpu/dma.h>
+/*
+ * Some of the SoCs feature two DMAC modules. In such a case, the
channels are
+ * distributed equally among them.
+ */
+#ifdef SH_DMAC_BASE1
+#define SH_DMAC_NR_MD_CH (CONFIG_NR_ONCHIP_DMA_CHANNELS /
2)
+#else
+#define SH_DMAC_NR_MD_CH CONFIG_NR_ONCHIP_DMA_CHANNELS
+#endif
+
+#define SH_DMAC_CH_SZ 0x10
+
/*
* Define the default configuration for dual address memory-memory
transfer.
* The 0x400 value represents auto-request, external->external.
@@ -29,7 +41,7 @@ static unsigned long dma_find_base(unsigned int chan)
unsigned long base = SH_DMAC_BASE0;
#ifdef SH_DMAC_BASE1
- if (chan >= 6)
+ if (chan >= SH_DMAC_NR_MD_CH)
base = SH_DMAC_BASE1;
#endif
@@ -40,13 +52,13 @@ static unsigned long dma_base_addr(unsigned int
chan)
{
unsigned long base = dma_find_base(chan);
- /* Normalize offset calculation */
- if (chan >= 9)
- chan -= 6;
- if (chan >= 4)
- base += 0x10;
+ chan = (chan % SH_DMAC_NR_MD_CH) * SH_DMAC_CH_SZ;
+
+ /* DMAOR is placed inside the channel register space. Step over
it. */
+ if (chan >= DMAOR)
+ base += SH_DMAC_CH_SZ;
- return base + (chan * 0x10);
+ return base + chan;
}
#ifdef CONFIG_SH_DMA_IRQ_MULTI
@@ -250,15 +262,11 @@ static int sh_dmac_get_dma_residue(struct
dma_channel *chan)
#define NR_DMAOR 1
#endif
-/*
- * 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) + \
- DMAOR)
+#define dmaor_read_reg(n) __raw_readw(dma_find_base((n) *
\
+ SH_DMAC_NR_MD_CH) +
DMAOR)
#define dmaor_write_reg(n, data) __raw_writew(data, \
- dma_find_base((n) *
6) + \
- DMAOR)
+ dma_find_base((n) *
\
+ SH_DMAC_NR_MD_CH) +
DMAOR)
static inline int dmaor_reset(int no)
{
```
Otherwise, I'll send it in separately. Of course we'll also need to fix
`SH_DMAC_BASE1` so that it's set only for SoCs that feature two DMAC
modules...
Cheers,
Artur
> Anyway, that's not new, so I have no objection to your patch.
>
> Gr{oetje,eeting}s,
>
> Geert
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