linux-kernel - Re: [PATCH 1/4] spi: cadence-quadspi: Flush posted register writes before INDAC access

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Message-ID: <mafs0y0quthdi.fsf@kernel.org>
Date: Thu, 04 Sep 2025 16:35:53 +0200
From: Pratyush Yadav <pratyush@...nel.org>
To: Santhosh Kumar K <s-k6@...com>
Cc: <miquel.raynal@...tlin.com>,  <broonie@...nel.org>,  <vigneshr@...com>,
  <marex@...x.de>,  <computersforpeace@...il.com>,
  <grmoore@...nsource.altera.com>,  <theo.lebrun@...tlin.com>,
  <linux-spi@...r.kernel.org>,  <linux-kernel@...r.kernel.org>,
  <praneeth@...com>,  <p-mantena@...com>,  <a-dutta@...com>,
  <u-kumar1@...com>,  Pratyush Yadav <pratyush@...nel.org>,
  <stable@...r.kernel.org>
Subject: Re: [PATCH 1/4] spi: cadence-quadspi: Flush posted register writes
 before INDAC access

Hi,

On Thu, Sep 04 2025, Santhosh Kumar K wrote:

> From: Pratyush Yadav <pratyush@...nel.org>
>
> cqspi_indirect_read_execute() and cqspi_indirect_write_execute() first
> set the enable bit on APB region and then start reading/writing to the
> AHB region. On TI K3 SoCs these regions lie on different endpoints. This
> means that the order of the two operations is not guaranteed, and they
> might be reordered at the interconnect level.
>
> It is possible for the AHB write to be executed before the APB write to
> enable the indirect controller, causing the transaction to be invalid
> and the write erroring out. Read back the APB region write before
> accessing the AHB region to make sure the write got flushed and the race
> condition is eliminated.
>
> Fixes: 140623410536 ("mtd: spi-nor: Add driver for Cadence Quad SPI Flash Controller")
> CC: stable@...r.kernel.org
> Signed-off-by: Pratyush Yadav <pratyush@...nel.org>
> Signed-off-by: Santhosh Kumar K <s-k6@...com>

IIRC I wrote this patch a few years ago when I was still at TI. Nice to
see it being upstreamed! It feels strange to review my own patch, but
FWIW,

Reviewed-by: Pratyush Yadav <pratyush@...nel.org>

[...]

-- 
Regards,
Pratyush Yadav