RE: [PATCH 1/3] mpt2sas: removetheuseofwriteq@xxxxxxx, since writeq is not atomic

["Desai, Kashyap" <Kashyap.Desai@xxxxxxx>]

Please ignore this patch.
Subject line is messed up.

I am going to resend with subject line fixed.


> -----Original Message-----
> From: linux-scsi-owner@xxxxxxxxxxxxxxx [mailto:linux-scsi-
> owner@xxxxxxxxxxxxxxx] On Behalf Of Kashyap, Desai
> Sent: Wednesday, May 04, 2011 4:34 PM
> To: linux-scsi@xxxxxxxxxxxxxxx
> Cc: James.Bottomley@xxxxxxxxxxxxxxxxxxxxx; Moore, Eric; Prakash, Sathya
> Subject: [PATCH 1/3] mpt2sas: removetheuseofwriteq@xxxxxxx, since
> writeq is not atomic
> 
> 
> The following code seems to be there in
> /usr/src/linux/arch/x86/include/asm/io.h.
> This is not going to work.
> 
> static inline void writeq(__u64 val, volatile void __iomem *addr)
> {
>         writel(val, addr);
>         writel(val >> 32, addr+4);
> }
> 
> So with this code turned on in the kernel, there is going to be race
> condition
> where multiple cpus can be writing to the request descriptor at the
> same time.
> 
> Meaning this could happen:
> (A) CPU A doest 32bit write
> (B) CPU B does 32 bit write
> (C) CPU A does 32 bit write
> (D) CPU B does 32 bit write
> 
> We need the 64 bit completed in one access pci memory write, else spin
> lock is required.
> Since it's going to be difficult to know which writeq was implemented
> in the kernel,
> the driver is going to have to always acquire a spin lock each time we
> do 64bit write.
> 
> Cc: stable@xxxxxxxxxx
> Signed-off-by: Kashyap Desai <kashyap.desai@xxxxxxx>
> ---
> diff --git a/drivers/scsi/mpt2sas/mpt2sas_base.c
> b/drivers/scsi/mpt2sas/mpt2sas_base.c
> index efa0255..5778334 100644
> --- a/drivers/scsi/mpt2sas/mpt2sas_base.c
> +++ b/drivers/scsi/mpt2sas/mpt2sas_base.c
> @@ -1558,7 +1558,6 @@ mpt2sas_base_free_smid(struct MPT2SAS_ADAPTER
> *ioc, u16 smid)
>   * care of 32 bit environment where its not quarenteed to send the
> entire word
>   * in one transfer.
>   */
> -#ifndef writeq
>  static inline void _base_writeq(__u64 b, volatile void __iomem *addr,
>      spinlock_t *writeq_lock)
>  {
> @@ -1570,13 +1569,6 @@ static inline void _base_writeq(__u64 b,
> volatile void __iomem *addr,
>  	writel((u32)(data_out >> 32), (addr + 4));
>  	spin_unlock_irqrestore(writeq_lock, flags);
>  }
> -#else
> -static inline void _base_writeq(__u64 b, volatile void __iomem *addr,
> -    spinlock_t *writeq_lock)
> -{
> -	writeq(cpu_to_le64(b), addr);
> -}
> -#endif
> 
>  /**
>   * mpt2sas_base_put_smid_scsi_io - send SCSI_IO request to firmware
> --
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