Re: [PATCH v2] spi-nor: intel-spi: Avoid crossing 4K address boundary on read/write

[Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>]

On Wed, Feb 27, 2019 at 09:57:15AM +0000, Sverdlin, Alexander (Nokia - DE/Ulm) wrote:
> It was observed that reads crossing 4K address boundary are failing.
> 
> This limitation is mentioned in Intel documents:
> 
> Intel(R) 9 Series Chipset Family Platform Controller Hub (PCH) Datasheet:
> 
> "5.26.3 Flash Access
> Program Register Access:
> * Program Register Accesses are not allowed to cross a 4 KB boundary..."
> 
> Enhanced Serial Peripheral Interface (eSPI)
> Interface Base Specification (for Client and Server Platforms):
> 
> "5.1.4 Address
> For other memory transactions, the address may start or end at any byte
> boundary. However, the address and payload length combination must not
> cross the naturally aligned address boundary of the corresponding Maximum
> Payload Size. It must not cross a 4 KB address boundary."
> 
> Avoid this by splitting an operation crossing the boundary into two
> operations.
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: Romain Porte <romain.porte@xxxxxxxxx>
> Tested-by: Pascal Fabreges <pascal.fabreges@xxxxxxxxx>
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxx>
> ---
> Changelog:
> v2:	More macros! As Mika suggested.
> 
>  drivers/mtd/spi-nor/intel-spi.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/mtd/spi-nor/intel-spi.c b/drivers/mtd/spi-nor/intel-spi.c
> index af0a220..8c279c4 100644
> --- a/drivers/mtd/spi-nor/intel-spi.c
> +++ b/drivers/mtd/spi-nor/intel-spi.c
> @@ -632,6 +632,10 @@ static ssize_t intel_spi_read(struct spi_nor *nor, loff_t from, size_t len,
>  	while (len > 0) {
>  		block_size = min_t(size_t, len, INTEL_SPI_FIFO_SZ);
>  
> +		/* Read cannot cross 4K boundary */
> +		blocksize = min(from + block_size, round_up(from + 1, SZ_4K)) -
> +			    from;

Nit:

It looks better if you put it into one line like:

		blocksize = min(from + block_size, round_up(from + 1, SZ_4K)) - from;


Regardless of that,

Acked-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>

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