From: Scott Branden <sbranden@broadcom.com>
To: Stephen Warren <swarren@wwwdotorg.org>,
Ulf Hansson <ulf.hansson@linaro.org>,
Russell King <rmk+kernel@arm.linux.org.uk>,
Peter Griffin <peter.griffin@linaro.org>,
Chris Ball <chris@printf.net>, Piotr Krol <pietrushnic@gmail.com>
Cc: linux-mmc@vger.kernel.org, linux-kernel@vger.kernel.org,
Joe Perches <joe@perches.com>,
linux-rpi-kernel@lists.infradead.org, Ray Jui <rjui@broadcom.com>,
bcm-kernel-feedback-list@broadcom.com
Subject: Re: [PATCHv2 3/5] mmc: shdci-bcm2835: add efficient back-to-back write workaround
Date: Fri, 7 Nov 2014 10:29:39 -0800 [thread overview]
Message-ID: <545D0F93.9080007@broadcom.com> (raw)
In-Reply-To: <545AFDB1.80008@wwwdotorg.org>
On 14-11-05 08:48 PM, Stephen Warren wrote:
> On 11/04/2014 11:55 PM, Scott Branden wrote:
>> On 14-11-04 08:57 PM, Stephen Warren wrote:
>>> On 10/30/2014 12:36 AM, Scott Branden wrote:
>>>> The bcm2835 has clock domain issues when back to back writes to certain
>>>> registers are written. The existing driver works around this issue with
>>>> udelay. A more efficient method is to store the 8 and 16 bit writes
>>>> to the registers affected and then write them as 32 bits at the
>>>> appropriate
>>>> time.
>>>
>>>> diff --git a/drivers/mmc/host/sdhci-bcm2835.c
>>>> b/drivers/mmc/host/sdhci-bcm2835.c
>>>
>>>> static void bcm2835_sdhci_writew(struct sdhci_host *host, u16 val,
>>>> int reg)
>>>> {
>>>> struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
>>>> - struct bcm2835_sdhci *bcm2835_host = pltfm_host->priv;
>>>> - u32 oldval = (reg == SDHCI_COMMAND) ? bcm2835_host->shadow :
>>>> - bcm2835_sdhci_readl(host, reg & ~3);
>>>> + struct bcm2835_sdhci_host *bcm2835_host = pltfm_host->priv;
>>>
>>> Is that type change for bcm2835_host really correct?
>>
>> Yes - at the top of the patch the structure has been expanded and named
>> appropriately.
>>
>> -struct bcm2835_sdhci {
>> - u32 shadow;
>> +struct bcm2835_sdhci_host {
>> + u32 shadow_cmd;
>> + u32 shadow_blk;
>> };
>
> Ah yes, sorry for missing that.
>
>>>> + } else {
>>>> + /* Read reg, all other registers are not shadowed */
>>>> + oldval = readl(host->ioaddr + (reg & ~3));
>>>
>>> Is there any reason to use readl() directly here rather than calling
>>> bcm2835_readl()? ...
>>
>> Yes, bcm2835_readl does not need to be called in read-modify-write and
>> shadow register situations and just adds overhead. All that needs to be
>> called is readl. bcm2835_readl has some existing ugly code in it to
>> modify the capabilities register on a read function. This info never
>> needs to be for write as you can't overwrite the capabilities register.
>
> To be honest, it seems better to do all the read/write through
> consistent functions. One advantage of bcm2835_readl() is that it
> consistently adds on the base address internally so you don't have to
> write it out every time manually. Still, the code ought to work fine
> after this change, so I guess it's OK.
>
>> I hope to get rid of the capabilities hack in a future patch as this
>> should never have been acceptable in upstreamed code to begin with. The
>> capabilities override should have been passed in through a device tree
>> entry.
>
> It's a pretty common technique with precedent. I certainly don't agree
> that it should be configured by DT. Arguably, DT makes sense to describe
> board-to-board variations, but there's almost zero point putting data
> into DT that is SoC description rather than board description; just put
> it into the driver to avoid continually parsing the same data over and
> over from DT just to get back to the same data that could have been
> encoded into the driver. If the data varies between similar controllers,
> an of_match table can easily be used to parameterize it based on
> compatible value.
There is work to be done here or I will be unable to use this driver in
our chipsets. Perhaps it will be easier having another driver
actually... as the DMA seems quite different on RPI.
>
next prev parent reply other threads:[~2014-11-07 18:29 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <Scott Branden <sbranden@broadcom.com>
2014-10-15 2:01 ` [PATCH 0/1] sdhci-bcm2835: added quirk and removed udelay in write ops Scott Branden
2014-10-15 2:01 ` [PATCH 1/1] mmc: " Scott Branden
2014-10-17 2:50 ` Stephen Warren
2014-10-15 16:43 ` Scott Branden
2014-10-18 2:37 ` Stephen Warren
2014-10-18 6:40 ` Scott Branden
2014-10-30 6:36 ` [PATCHv2 0/5] " Scott Branden
2014-10-30 6:36 ` [PATCHv2 1/5] mmc: sdhci-bcm2835: group read and write functions to improve readability Scott Branden
2014-10-30 6:36 ` [PATCHv2 2/5] mmc: sdhci-bcm2835: make shift calculations consistent Scott Branden
2014-11-05 4:48 ` Stephen Warren
2014-11-05 5:19 ` Scott Branden
2014-10-30 6:36 ` [PATCHv2 3/5] mmc: shdci-bcm2835: add efficient back-to-back write workaround Scott Branden
2014-11-05 4:57 ` Stephen Warren
2014-11-05 6:55 ` Scott Branden
2014-11-06 4:48 ` Stephen Warren
2014-11-07 18:29 ` Scott Branden [this message]
2014-10-30 6:36 ` [PATCHv2 4/5] mmc: shdci-bcm2835: add verify for 32-bit back-to-back workaround Scott Branden
2014-11-05 4:44 ` Stephen Warren
2014-11-05 5:26 ` Scott Branden
2014-11-05 4:59 ` Stephen Warren
2014-11-05 7:00 ` Scott Branden
2014-11-06 5:01 ` Stephen Warren
2014-11-07 18:31 ` Scott Branden
2015-12-22 15:55 ` Stefan Wahren
2015-12-22 19:23 ` Scott Branden
2015-12-22 20:13 ` Stefan Wahren
2014-10-30 6:36 ` [PATCHv2 5/5] mmc: sdhci-bcm2835: add sdhci quirk SDHCI_QUIRK_MULTIBLOCK_READ_ACMD12 Scott Branden
2014-11-05 5:00 ` Stephen Warren
2014-11-05 7:02 ` Scott Branden
2014-11-06 4:50 ` Stephen Warren
2014-11-07 18:30 ` Scott Branden
2014-12-05 0:11 ` [PATCH] mmc: sdhci: add quirk for ACMD23 broken Scott Branden
2014-12-05 0:16 ` [PATCH v2] " Scott Branden
2014-12-17 18:36 ` Scott Branden
2014-12-17 19:48 ` Chris Ball
2014-12-17 20:42 ` Scott Branden
2015-02-10 0:06 ` [PATCH 0/4] Add support for IPROC SDHCI controller Scott Branden
2015-02-10 0:06 ` [PATCH 1/4] mmc: sdhci: add quirk for ACMD23 broken Scott Branden
2015-02-10 0:06 ` [PATCH 2/4] mmc: sdhci: do not set AUTO_CMD12 for multi-block CMD53 Scott Branden
2015-02-10 0:06 ` [PATCH 3/4] mmc: sdhci-iproc: add IPROC SDHCI driver Scott Branden
2015-02-10 0:06 ` [PATCH 4/4] mmc: sdhci-iproc: add device tree bindings Scott Branden
2015-03-02 23:50 ` Florian Fainelli
2015-03-04 23:14 ` Scott Branden
[not found] ` <1423526791-29453-1-git-send-email-sbranden-dY08KVG/lbpWk0Htik3J/w@public.gmane.org>
2015-02-26 17:28 ` [PATCH 0/4] Add support for IPROC SDHCI controller Scott Branden
2015-03-05 15:59 ` [PATCH RESEND " Scott Branden
2015-03-05 15:59 ` [PATCH 1/4] mmc: sdhci: add quirk for ACMD23 broken Scott Branden
2015-03-05 15:59 ` [PATCH 2/4] mmc: sdhci: do not set AUTO_CMD12 for multi-block CMD53 Scott Branden
2015-03-05 15:59 ` [PATCH 3/4] mmc: sdhci-iproc: add IPROC SDHCI driver Scott Branden
2015-03-05 15:59 ` [PATCH 4/4] mmc: sdhci-iproc: add device tree bindings Scott Branden
2015-03-05 16:16 ` [PATCH RESEND 0/4] Add support for IPROC SDHCI controller Ulf Hansson
2015-03-05 19:57 ` Florian Fainelli
2015-03-10 18:35 ` [PATCH] mmc: sdhci: fix card presence logic in sdhci_request function Scott Branden
2015-03-13 10:14 ` Ulf Hansson
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