[PATCH] Revert "spi: cadence-qspi: Improve spi memory performance"

[PATCH] Revert "spi: cadence-qspi: Improve spi memory performance"

[Miquel Raynal]

During the v6.14-rc cycles, there has been an issue with syscons which
prevented TI chipid controller to probe, itself preventing the only DMA
engine on AM62A with the memcpy capability to probe, which is needed for
the SPI controller to work in its most efficient configuration.

The SPI controller on AM62A can be used in DAC and INDAC mode, which are
some kind of direct mapping vs. CPU-controlled SPI operations,
respectively. However, because of hardware constraints (some kind of
request line not being driven), INDAC mode cannot leverage DMA without
risking to underflow the SPI FIFO. This mode costs a lot of CPU
cycles. On the other side however, DAC mode can be used with and without
DMA support, but in practice, DMA transfers are way more efficient
because of the burst capabilities that the CPU does not have.

As a result, in terms of read throughput, using a Winbond chip in 1-8-8
SDR mode, we get:
- 3.5MiB/s in DAC mode without DMA
- 9.0MiB/s in INDAC mode (CPU more busy)
- a fluctuating 9 to 12MiB/s in DAC mode with DMA (a constant 14.5MiB/s
  without CPUfreq)

The reason for the patch that is being reverted is that because of the
syscon issue, we were using a very un-efficient DAC configuration (no
DMA), but since:

commit 5728c92ae112 ("mfd: syscon: Restore device_node_to_regmap() for non-syscon nodes")

the probing of the DMA controller has been fixed, and the performances are
back to normal, so we can safely revert this commit.

This reverts commit 6e6363dd2f1e5b3e42505606ea494572c81dbb64.

Suggested-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
---
 drivers/spi/spi-cadence-quadspi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/spi/spi-cadence-quadspi.c b/drivers/spi/spi-cadence-quadspi.c
index 559fbdfbd9f7..c90462783b3f 100644
--- a/drivers/spi/spi-cadence-quadspi.c
+++ b/drivers/spi/spi-cadence-quadspi.c
@@ -2073,7 +2073,7 @@ static const struct cqspi_driver_platdata k2g_qspi = {
 
 static const struct cqspi_driver_platdata am654_ospi = {
 	.hwcaps_mask = CQSPI_SUPPORTS_OCTAL | CQSPI_SUPPORTS_QUAD,
-	.quirks = CQSPI_DISABLE_DAC_MODE | CQSPI_NEEDS_WR_DELAY,
+	.quirks = CQSPI_NEEDS_WR_DELAY,
 };
 
 static const struct cqspi_driver_platdata intel_lgm_qspi = {
-- 
2.48.1

Re: [PATCH] Revert "spi: cadence-qspi: Improve spi memory performance"

[Mark Brown]

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On Fri, Mar 28, 2025 at 06:35:00PM +0100, Miquel Raynal wrote:

> the probing of the DMA controller has been fixed, and the performances are
> back to normal, so we can safely revert this commit.

> This reverts commit 6e6363dd2f1e5b3e42505606ea494572c81dbb64.

This commit doesn't appear to exist, you seem to mean cce2200dacd6 (spi:
cadence-qspi: Improve spi memory performance), I fixed it up for that.

Please submit patches using subject lines reflecting the style for the
subsystem, this makes it easier for people to identify relevant patches.
Look at what existing commits in the area you're changing are doing and
make sure your subject lines visually resemble what they're doing.
There's no need to resubmit to fix this alone.

Please include human readable descriptions of things like commits and
issues being discussed in e-mail in your mails, this makes them much
easier for humans to read especially when they have no internet access.
I do frequently catch up on my mail on flights or while otherwise
travelling so this is even more pressing for me than just being about
making things a bit easier to read.

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Re: [PATCH] Revert "spi: cadence-qspi: Improve spi memory performance"

[Miquel Raynal]

Hi Mark,

On 31/03/2025 at 14:24:19 +01, Mark Brown <broonie@kernel.org> wrote:

> On Fri, Mar 28, 2025 at 06:35:00PM +0100, Miquel Raynal wrote:
>
>> the probing of the DMA controller has been fixed, and the performances are
>> back to normal, so we can safely revert this commit.
>
>> This reverts commit 6e6363dd2f1e5b3e42505606ea494572c81dbb64.
>
> This commit doesn't appear to exist, you seem to mean cce2200dacd6 (spi:
> cadence-qspi: Improve spi memory performance), I fixed it up for that.

Crap, must have catch the one from my own local tree, thanks for fixing.

> Please submit patches using subject lines reflecting the style for the
> subsystem, this makes it easier for people to identify relevant patches.

I'm curious, maybe this is a semi-automated message, but do you have a
specific style for reverts that deviates from git's?

> Look at what existing commits in the area you're changing are doing and
> make sure your subject lines visually resemble what they're doing.
> There's no need to resubmit to fix this alone.
>
> Please include human readable descriptions of things like commits and
> issues being discussed in e-mail in your mails, this makes them much
> easier for humans to read especially when they have no internet access.
> I do frequently catch up on my mail on flights or while otherwise
> travelling so this is even more pressing for me than just being about
> making things a bit easier to read.

As per the "This reverts commit <sha>" this is also the standard Git way
to indicate a revert, I kept it as-is.

Thanks,
Miquèl

Re: [PATCH] Revert "spi: cadence-qspi: Improve spi memory performance"

[Mark Brown]

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On Tue, Apr 01, 2025 at 11:56:50AM +0200, Miquel Raynal wrote:
> On 31/03/2025 at 14:24:19 +01, Mark Brown <broonie@kernel.org> wrote:

> > Please submit patches using subject lines reflecting the style for the
> > subsystem, this makes it easier for people to identify relevant patches.

> I'm curious, maybe this is a semi-automated message, but do you have a
> specific style for reverts that deviates from git's?

Reverts are just normal changes and should have normal changelogs that
follow the standard style for changelogs.

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